Competitive Inhibitor for Inhibiting the Methylation of Protein Phosphate 2a via LCMT-1 - Essay Example

Competitive inhibitor for inhibiting the methylation of Protein phosphate 2A (PP2A) Via LCMT Table of Contents Table of Contents 2Structure of PP2A 3 Regulation of Protein Phosphatase 2A (PP2A) 4 Effect of PP2A 4 LCMT1 6 The role of LCMT1 in regulation of PP2A 6 Localization of LCMT1 6 Effect and functions 7 Complexity of the interaction between LCMT1 and PP2A 8 Importance of effecting the activity of LCMT1 9 Phosphorylation 9 PP2A & LCMT-1 Complexes  11 Computer Aided Drug Design (CADD) 12 Molecular Modeling 13 Molecular docking techniques 14 Protein Databank 15 References 17 PP2A According to Tamanoi and Clarke (2006, p.315), PP2A has the role of controlling of cell cycle progression, especially during mitosis phase of the cell. In their view, little is known concerning the biochemical basis of the regulation of PP2A activity during the cell cycle. A substantial amount of PP2A is usually in the methylated form and range from 70 to 93%, which depend of the particular method utilized in the evaluation of the level of methylation. Methylation of the PP2A is considered important for the binding process of the B subunits that commonly target PP2A for differentiation of substrate and specific cellular compartments. This means that the methylation of PP2A may be an important regulatory mechanism on the condition that the PP2A methylation is tightly regulated. Tamanoi and Clarke (2006, p. 316) further presents that there are two main levels of regulation of the PP2A. This is may be achieved either through demethylating enzyme LCMT1 or PME-1 or the regulation at the C-terminal tail of PP2AC site (Tamanoi and Clarke, 2006, p. 316). Furthermore, they advance that the methylation of PP2A can also be regulated or deregulated by certain diseases(Sheng 2013). Seshacharyulu, Pandey, Datta and Batra (2013, p.9) elaborates that PP2A serves to regulate the function by dephosphorylating numerous important cellular molecules such as the p53 and Akt. The PP2A is significant in critical cellular processes including signal transduction, proliferation and apoptosis. Structure of PP2A PP2A is structurally multifarious made up of catalytic, support and regulatory subunits. The support and catalytic sub-units of the PP2A comprise of two major isoforms, whereas the regulatory sub-unit has four distinct families of different isoforms. Of these sub-units, the regulatory sub-unit is considered the most diverse in terms of spatial and temporal specificity. The PP2A usually undergoes certain post-translational changes such as methylation and phosphorylation that serve to regulate the enzymatic activity of PP2A. Certain somatic alterations, mutations and aberrant expression of the PP2A support and regulatory sub-units have been common in a variety of malignancies in humans including skin, breast and lung cancers. This demonstrates that the role of PP2A as a tumor suppressor (Seshacharyulu et.al 2013). A group of heterogeneous genes encode the individual subunits of the enzyme. This gives rise to a multitude of various PP2A holoenzyme complexes (Schönthal 2013, p.2). Some of the observations that PP2A puts certain stimulatory and inhibitory effects on the cells growth can, therefore, be attributed to the various activities of some of the different activities of PP2A complexes that have unique subcellular locations and substrate specificities. Regulation of Protein Phosphatase 2A (PP2A) Protein Phosphatase 2A (PP2A) is purported to be involved in cell growth and proliferation events. It may also be associated with tumour progression. PP2A belongs to the serine/threonine (Ser/Thr) phosphatase group. The activity of this protein is commonly regulated by a wide range of mechanisms. Effect of PP2A The PP2A has certain specific functions in the neuronal cells. This is based on the high expression of the PP2A isoforms in the brain. As such, Tamanoi and Clarke suggest that PP2A is involved in the regulation of the phosphorylation state of neuronal-specific microtubule-associated proteins that play a significant role in the regulating microtubule stability. They also indicate that there is was evidence that points PP2A’s role in the progression of Alzheimer’s disease. Commonly, Alzheimer’s disease is indicated by the presence of two distinct histopathological marks such as the neurofibrillary tangles. They consist of abnormally hyperphosphorylated tau, assembled as a pair of helical filaments. A group of PP2A is associated with microtubules that bind and dephosphorylate the tau protein-associated microtubule. Further evidence indicates that the expression of LCMT1 and PP2A methylation levels are commonly decreased in Alzheimer disease. This indicates the crucial role of methylated PP2A in the disease. Moreover, methylated PP2A plays a role in the secretion of insulin. (DMello, 2012, p.181) points to several studies that indicate that PP2A has a role to play in the stimulation of secretion of insulin. One such evidence is the fact that key signalling proteins of the insulin exocytotic flow tend to be retained in their phosphorylated state, which is linked with stimulation of insulin secretion. An inhibition of demethylation of PP2A by a methylesterase inhibitor such as ebelactone, subsequently resulted in the inhibition of secretion of insulin from some isolated cells. In insulin secreting pancreatic cells, it was established that glucose and calcium tend to reduce the methylation of PP2A. In general, this provide evidence that methylation of PP2A has an important regulatory role in the sequence of events that results in the secretion of insulin as evident in the fact that a reduction of methylation of PP2A resulted in a decrease of holoenzyme assembly. Effecting of the activityof PP2A is, therefore crucial owing to its critical involvement in the control of cellular growth, as well as the control of potential development of cancer. Schönthal (2011 pg. 2) points out that several studies demonstrate that the enzyme exert tumour suppressive function. Subsequently, other studies have also indicated the requirement of the enzyme in the growth and survival of the cell. LCMT1 Lee and Pallas (20072007, p.30974) demonstrates a study that shows the importance leucine carboxyl methyltransferase – 1 (LCMT1). They point out that LCMT1 is particularly important in PP2A methylation and cell function. The role of LCMT1 in regulation of PP2A To begin with, one of the most common mechanisms is the reversible methylation involving select methyltransferases. Leucine carboxyl (LCMT1), commonly known as PPMT1 or CGI68, a member of the 334 amino acid group belonging to the methytransferase superfamily, is also involved in the regulation of the PP2A. In particular, the LCMT1 serves to catalyse the methylation process of the carboxyl group of the PP2A’s C-terminal luecosine. Due the ability of LCMT1 to regulate the functioning of PP2A, LCMT1 is regarded critical for mitotic progression of a cell and the general survival of the cell. LCMT1 is commonly recommended for the detection of LCMT1 of human origin by Western Blotting, immunosuppression, and immunofluorescence. Localization of LCMT1 Considering that the role of LMT1 is to regulate the methylation of PP2A, it is important for strict control of the methlating and demethytlating of PP2A. In the cell, this is commonly established by different subcellular localization of the enzymes, LCMT1 included. For instance, GFP-fusing protein tests of LCMT1 reveals that LCMT1 is abundantly localized in the cytoplasm. This localization can also be confirmed using the in vivo immunofluorescence with antibodies against the endogenous LCMT1 that confirms the specific localization. One study indicated that a reduction of LCMT1 protein levels using a small hairpin RNA can cause up to 70% reduction of methylation of PP2A in HeLa cells. This indicates that LCMT1 is one of the major PP2A methyltransferase. Subsequently, another study on a subset of cells indicated that a reduction in LCMT1 levels consequently reduced the formation of PP2A heterotrimers that contain the regulatory subunit, which induced apoptosis depicted by nuclear fragmentation and caspase activation, as well as membrane blebbing (Lee and Pallas 2007). A reduction of the PP2A regulatory subunit also produces a similar level of apoptosis indicating that LCMt1 causes apoptosis partly by causing a disruption in the formation of PP2A heterotrimers. Nevertheless, treatment of the cells with a pan-caspase inhibitor reduced apoptosis caused by a reduction of LCMT1. In addition, Lee and Pallas (2007) point out that, cells with reduced LCMT1 tend to be rather sensitive to spindle-targeting drugs such as nocodazole. This implies that LCMT1 is crucial for spindle checkpoint during mitosis. Effect and functions Leucine Carboxyl Methyltransferase -1 (LCMT1) serves to methylate the carboxyl group of the C-terminal leucine residue of the PP2A catalytic subunits, which results in the formation of the alpha-leucine residues. It belongs to the LCMT family and the methyltransferase superfamily. Thiriet (2011, p.269) points out that other than the reversible methylation of nucleic bases of DNA, various amino acids of proteins undergo methylation. As such, many classesof protein carboyl methyltransferases tend to exist based on the methyl group acceptor. The methyltransferases usually act promote the formation of heterochromatin by methylating histone protein tails, LCMT1, as common methyltransferace, causes reversible carboxyl methylation of C-terminal leucine of catalytic subunit of PP2A. The main function of LCMT1 centers on the regulation of methylation of PP2A, which is a critical process in differentiation of neuroblastoma cells (Anon., 2011). Methylation of PP2A catalytic C subunit by the LCMT1 is a critical PP2A regulatory mechanism.Martínez (2010, p.195) is of the opinion that LCMT1 modulates the formation of PP2A hooenzymes that commonly contain the Ba sub-unit responsible for the dephosphorylation of major neuronal cytoskeletal proteins such as the Tau. One study revealed that enhanced expression of LCMT1 in a cultured N2a neuroblastoma cells induces certain changes in F-actin organization. This in turn promotes serum-independent neuritogenesis and subsequent development of extended tau-positive processes in cell differentiation. Mackay et.al (2013, p.2) elaborates that LCMT1 is a class 1 S-adenosylmethionine-dependent methyltransferase with PP2 as its only known substrate. In a study involving mice, a knockdown of LCMT1 in rats was identified to be lethal, particularly during the embryonic development stages. LCMT in conjunction with the predominantly nuclear methylesterase PME1 catalyzes carboxyl methylation of the C-terminus at L309 (MacKay et.al 2013, p.2). The L309 carboxyl methylation catalyzed by LCMT1 is deemed necessary for binding of the B alpha subunit. Consequently, this positively influences the binding of the B family subunits that are presumed to provide protection against oncogenic transformation. Stanevich et.al (2012) observes that a dominant-negative LCMT1 mutant reduces the cell cycle without cell death. This is likely to be as a result of inhibition of uncontrolled phosphatase activity. Complexity of the interaction between LCMT1 and PP2A Regarding the complexity of the interaction between LCMT1 and PP2A, (DMello, 2012, p.180) postulates that neither PP2A loss-of-function mutants, which have their active site residues mutated, nor the wild-types that have been subjected to protein inhibitors, can be methylated by LCMT1. Moreover, peptides that mimic the C-terminal tail of the PP2A cannot be LCMT1 substrates. This shows the specificity of LCMT1. Sents, Ivanova, Lambrecht, Haesen and Janssens (2011, p.645) explain that recent co-crystal structures study of LCMT1 with the catalytic subunit PP2Ac provide some insights on the complex protein interaction. The study further reveals that based on the surface interactions between the active site of the methyltransferase and the C-terminal tail of the PPA2, as well as the communication between the LCMT1 domain and the PPA2 catalytic subunit,LCMT1 plays an additional role in minimizing the activity of free PP2A catalytic subunit. This is achieved through selective enhancement of methylation of the activated PPA2 and the subsequent conversion into appropriate trimeric holoenzymes. Importance of effecting the activity of LCMT1 Mackay et.al (2013, p. 3) undertook a study that emphasizes on the need to make improve the activity of LCMT1. In their study, they reported that the generation of a LCMT1 hypomorhpic mouse model indicating the biochemical and the phenotypic effects of reduced LCMT1 activity. They observed a decrease in PP2A methylation in a simultaneous increase in demethylation in the LMCT1 hypomorphic mice. They also observed a decrease in glucose tolerance, as well as an increase in glucose-stimulated insulin secretion. On the other hand, Sontag, Craig, Mitterhuber, Ogris and Sontag (2010, p. 1455), suggest that LCMT1 expression and activity might be synchronized by changes in homocysteine metabolism. This in itself is exaggerated by nutritional intake of vitamins B6 and B12 and folate. This implies that a deficiency in these vitamins may cause elevated homocysteine levels in the plasma and subsequent impairment of holoenzyme assembly that contribute to various ailments such as Alzheimer’s disease and cancer. Phosphorylation Phosphorylation is one of the means of attachment of small chemical groups (Thiriet 2011, p.266). It was among the first means of post-translational protein modification to be discovered. In phosphorylation, kinases and phosphates attach and remove the phosphate group to target proteins. Correspondingly a protein can have any phosphorylation sites. Each of the phosphorylation sites can be a target of a number of kinases that either activate or inactivate the functioning of the protein. Phosphorylation is another procedure through which enzymes can be controlled. The procedure stimulates structural change that controls an enzyme activity, commonly in eukaryotic cells. The procedure involves a variety of protein kinase and phosphatase, which are dependent on the protein phosphorylation activity, also referred to as the phosphorylation cycle. Phosphorylation usually adds a phosphate group to a side chain or removes the phosphate group from the chain. The phosphate group in eukaryotic cells is covalently attached to an amino acid chain. The negative charge of the phosphate is associated with a change in the conformational shape of the protein that results in the alteration of the proteins’ action. Protein phosphorylation involves the use of protein kinase that serves as a catalyst. Subsequently, the phosphate group from the ATP is then transferred to a hydroxyl group of the protein chain. A reversible process is also possible, in which the phosphate groups are removed from the protein side chain using PP2A enzyme as the main catalyst. This process is known as dephosphorylation. Prior to the phosphorylation of proteins, protein Tyrokinases are first activated by autophosphorylation of their own specific tyrosine residues. The activation ten involves the displacement of an amino acid loop, which initially blocks access to the active sites, but moves away upon phosphorylation (Gaplovska-Kysela & Sevcovicova, 2013, p. 716). Reversible phosphorylation produces an on-off switch and also fine tunes the transactivating potential of transcription factors, as well as the nuclear factor of activated T-cells. Similarly, multiple phosphorylation enables signal integration. Tightly controlled protein phosphorylation and dephosphorelation is considered critical for effective cellular function in mammalian cells. In particular, the extent of phosphorylation at a given site tends to be balanced by the opposing actions of protein phosphates and kinases (MacKay, Tu, Young and Clarke 2013 p.2). Nearly a third of human proteome is regarded to phosphorylated by nearly 518 human protein kinases at tyrosine residues. The phosphorylation of tyrosine is usually catalyzed by protein tyrosine kinases that are coded for by nearly 90 genes in human genome. PP2A is the major serine/threonine protein phosphatase that recognizes a wide variety of substrates that are involved in many signaling flows and cellular functions (MacKay et.al 2013, p.2). PP2A & LCMT-1 Complexes  PP2A and LCMT1 commonly produce unstable heterogeneous complexes that cannot form crystals. The inability of the PP2A crystals to form crystals is also associated with the soft environment at the active site of the enzyme. Nonetheless, the crystallization of the PP2A-LCMT1 complex can be achieved through the synthesis of SAM. SAM facilitates the process by binding covalently at the PP2A tail before forming the stable PP2A-LCMT1 complex. The complex formed provides a clear perception of the structure of the complex and the possible interactions involved in the formation of the structure, such as the active site. According to a Stanevich et.al (2012) study of the human LCMT1 structure in isolation and the PP2A-LCMT1 complex structures, it was revealed that the LCMT1 structure in isolation has an active site pocket that recognizes the carboxyl tail of the PP2A. Subsequently, they also observed that the active site pockets of the PP2A can makes the extensive contacts to the LCMT1 to form a complex that is stabilized by a co-factor mimic. They also ascribe the malleable nature of the active of the PP2A and the complex heterogeneity of the complex as the likely factors that hinder crystallization of the complex. The idea was derived from the fact that in vitro methylation yielded only a fraction of PP2A (Schönthal, 2001, p. 3). Facilitating crystallization of the complex can, however be achieved by synthesizing a SAM mimic. The SAM mimic covalently bounds to the tail of PP2A in catalysis. The resultant PP2A-LCMT1 complex is relatively stable and be co-purified using the anion exchange chromatography. The complex can also be separated from the PP2A fraction that failed to undergo methylation (Stanevich 2011). In addition, the diffracting crystals can be obtained by the introduction of an internal truncation in the PP2A tail into the complex.A review of the PP2A-LCMT1 complex indicates that the lid domain of the LCMT1 forms extensive contacts to the PP2A tail and active site as shown below; Computer Aided Drug Design (CADD) Computational aided drug designs are techniques that are widely used in the bioinformatics and chemoinformatics. Most drugs produce their effects by interacting with largest molecules through a variety of interactions. These interactions are, however, rather involving and require a lot of calculations and require specialized techniques. The potentials of these drugs depend on their binding affinity. With such a large number of such drugs that require measurement of the relative potency, presents a rather difficult task. CADD techniques provide a means making this task easy. Two main types of Computer aided drug designs exists; analogue or ligand based design and structural or target based design. Although the two designs are different from each other, they can be used concurrently or individually depending on the intended purpose. The ligand based design mainly utilizes the quantitative structure activity relationship or the pharmacophore maps. These are used to identify and edit a lead compound without necessarily having to know the exact 3D structure of the corresponding receptor. The design also commonly keeps the functional groups on the 3D structure on a scaffold that is deemed crucial for the activity of the already existing ligands. When a ligand and protein fit, they are taken through molecular docking. On the other hand, structural based design is considered as a drug design for compound discovery and optimization. The design has been integral towards the discovery of new classes of compounds. In particular, the design has shade more light for the analysis of the crystal structures of complexes of proteins and ligands. The design has also provided a means for the determination of protein-ligand interactions. The design employs two main approaches; the de novo design and the molecular docking. Structure-based drug design most clearly exploits the concept of 3-d binding sites that interact with ligands, an area that the computations methods and models play a critical role. Broorijmans (2009, p.636) explains that in the structure0-based drug design. The predicted shape of the binding site is used to optimize the ligand to best fit the receptor. He also affirms that the driving forces of thee specific interactions in biological site surfaces are drive by the complementariness in both shape and electrostatic of the surfaces of the binding sites and the substrate or ligand. Modern drug discovery cycle commonly begin with the identification of a biological target most often a protein that is known to play a critical role in the development of a particular disease. The biological attempts are then developed that can measure the inhibition or activation of the target of interest by small molecules either in vivo or in vitro. The test evaluates thousands of molecules in a high-throughput screening (HTS) that tests each compound once in a single dose yielding a percent inhibition value (Broorijmans 2009, p.636). The dose that yields a high percent inhibition value is confirmed as the successful. Pharmaceutical firms usually screen their entire collection of molecules in the examination against the target to identify the possible leads. This, therefore, demonstrates the importance of a protein bank. Molecular Modeling Moreover, molecular modelling allows gathering of quantitative information regarding the molecular geometries that in turn provide information about the bond angles, surface area, and the energy and of the atoms and the distance between the individual atoms. Computer aided drug design have offered a great improvement in drug designing with a potential chance of reducing the cost of drug designing by up to 50%. CADD has also provided several alternatives for generation of biologically active molecules. Molecular modeling is also a binding design that utilizes a variety of computer integrated software to determine the binding efficacy. One of the common molecular modeling techniques is the use of Scigress design. The Scigress is molecular modeling software that allows the visualization and building a variety of structures using a multifunctional tool that allows importation of experiment structures(FQS, 2014). Conversely, Scigress also poses the unique ability to apply a variety of computational models such as molecular mechanics involving various types of molecular systems such as whole proteins, organic molecules and polymers, among others. The technique facilitates the composition of numerous potential protein ligands. This allows for the placement of any bonds and the creation protein ligands and subsequently allow for the computation of the correct geometries and conformations. The method also allows one to increase the binding activity where possible. Molecular docking techniques The binding of molecule ligands to their large protein targets is vital for various biological processes (Taylor, Jewsbury and Essex 2002, p.151). The binding requires accuracy of high level, which requires accurate prediction of the modes of protein-ligand protein, otherwise referred to as the docking problems. Modern structure-based drug designing have developed various docking techniques. Molecular docking, also known as semi flexing, usually commences after drawing and creation of the all the molecules on a program. The program subsequently suggests the various binding forms of protein inhibitors, in addition to evaluation of the binding geometries of a theoretical ligand with an unknown structure (Tramontano, 2007). The varieties of docking methods are usually assessed based on their ability to dock large number of small molecules in a receptor’s binding site (Conn, 2003, p. 93). Molecular docking mainly involves three main steps. To begin with, the binding site should be characterized prior to the positioning the ligand into the site(Dias & Azevedo, 2008, p. 1041). This is then followed by measuring the strength of the interaction by the value of the produced energy. Common molecular docking methods follow a basic docking procedure. Each ligand is docked into the active site of the enzyme’s active site and confirming the binding score to evaluate whether the ligand fits accurately to the active site (Taylor, et al., 2002, p. 151). The binding score refers to the energy of interaction that is emitted during the binding process. A higher energy value indicated a stronger bond between the ligand and the active site, which consequently imply a stronger inhibitor(Sharma, 2010, p. 63). Castro and Laghi (2011, p.334) point out that molecular docking attempts to envisage the organization of the intermolecular complex created by molecules. The procedure is widely used to suggest the binding mode of bioactive inhibitors. The docking algorithms generate different possible modes of binding of inhibitors for a selected target, which are further ranked according to the docking score filtering criteria(Mukesh & Rakesh, 2011, p. 1747). Protein Databank A protein data bank is a worldwide archive if structural data of various biological macromolecules (Bernman 1999, p.235). The protein data bank usually archives nearly all published 3D macromolecule structures that of medical relevance. The protein bank is mostly recognized for its expansive archive of depositories of X-Ray crystal structures, protein structures and bio-molecules that are approximated at 72,884 structures (Berman, et al., 2000, p. 899). Initial use of the PDB was limited to a rather small group of experts involved in structural research. However, this has changed over time with depositors to bank having varied expertise in the techniques such as nuclear magnetic resonance (NMR), X-Ray crystal and cryoelectron (Bernman 1999, p.235). Researches in biology, chemistry or computer science and students at all levels can access the PDB. The main goal of a PDB is to create a resource that is based on the most modern technology that facilitates the use and subsequent analysis of structural data (Parasuraman, 2012, p. 351). This will create an empowered resource for biological resource. Efficient capture and presentation of data is a critical component for the creation of public information archive. The process capturing data and presentation generally entails data deposition, annotation and validation (Lipkowitz & Boyd, 2001, p. 5). The data can be submitted to the PDB through email or via an AutoDep Input tool (ADIT). The ADIT processes the entries and has an integrated dictionary known as the mmCIF dictionary that provides the ontology of the numerous terms that define a macromolecular structure and the subsequent crystallographic experiment (Westbrook, et al., 2003, p. 490). The system ensures that the submitted data are consistent with the mmCIF dictionary definitions of the data terms, and subsequently enumerates the range of allowable values and relationships between data values. To deposit an entry into the PDB, a PDB identifier is usually sent to the author of the particular structure. The identifier includes information pertaining to the structure, which is loaded into the internal core database of the PDB before being validated for any errors. Following the review of the processed file, the author is allowed to send a revision, which may be repeated severally. Successful revisions are then approved and entered into the internal core database ready for distribution. References Anon., 2011. Issues in Neuroscience Research and Application: 2011 Edition. Atlanta, Georgia: Scholarly Editions. Berman, H. M. et al., 2000. The Protein Data Bank. Acta Crystallographica , 58(6), pp. 899 - 907 . Berman, H. N. et al., 2000. The Protein Data Bank. Nucleic Acid research, 28(1), pp. 235-242. Brooijmans, N., 2009. Docking Methods, Ligand Design, And Validating Data Sets In The Structural Genomics Era. Structural Bioinformatics, pp. 635-632. Castro, E. A. & Haghi, A. K., 2012. Advanced Methods and Applications in Chemoinformatics: Research Progress and. Hershy, PA: Idea Group Inc (IGI). Conn, M., 2003. Receptor-Receptor Interactions: Methods in Cell Biology. 17 ed. Waltham, MA: Academic Press. Dias, R. & Azevedo, W. d., 2008. Molecular Docking Algorithms. Current Drug Targets, , 9(12), pp. 1040-1045. DMello, F., 2012. Amino Acids in Human Nutrition and Health. Cambridge, MA: CABI. FQS, 2014. SCIGRESS - Molecular modeling software. [Online] Available at: www.fqs.pl/chemistry_materials_life_science/products/scigress [Accessed 27 February 2014]. Gaplovska-Kysela, K. & Sevcovicova, A., 2013. Phosphorylation: a key regulator of meiosis. Cell cycle, 12(5), p. 716. Hua, S. W., Sheng, X. Y. & Bao, X., 2003. Protein phosphatase 2A: its structure, function and activity regulation. Pubmed, 35(2), pp. 105-112. Jiang, L. et al., 2013. Structural basis of protein phosphatase 2A stable latency. Nature Communications, Volume 4, p. 1699. Lee, J. A. & Pallas, D. C., 2007. Leucine carboxyl methyltransferase-1 is necessary for normal progression through mitosis in mammalian cells.. Journal of Biological Chemistry, 282(42), pp. 30974-84. Lipkowitz, K. B. & Boyd, D. B., 2001. Reviews in Computational Chemistry, Reviews in Computational Chemistry. 17 ed. New York: John Wiley & Sons. Liu, F., Grundke-Iqbal, I., Iqbal, K. & Gong, C.-X., 2005. Contributions of protein phosphatases PP1, PP2A, PP2B and PP5 to the regulation of tau phosphorylation. The European journal of neuroscience, 22(8), pp. 1942-1950. MacKay, K. B., Tu, Y., Young, S. G. & Clarke, S. G., 2013. Circu mventing Embryonic Lethality with Lcmt1 Deficie ncy: Gen eration of Hypomorphic Lcmt1 Mice with Redu ced Protein Phosphatase 2A Methyltransf erase Expression and Defects in Insulin Sig naling. PLoS ONE, 8(6), pp. 1-12. Martínez, A., 2010. Emerging Drugs and Targets for Alzheimers Disease: Beta-Amyloid, Tau and glucose metabolism. Cambrige, U.K: Royal Society of Chemistry. Mukesh, B. & Rakesh, K., 2011. Molecular Dcoking; A Review. International Journal of Research in Ayurveda and Pharmacy, 2(6), p. 1746-1751. Parasuraman, S., 2012. Protein Databank. Journal of pharmacology & pharmacotherapeutics, 3(4), p. 351. Schönthal, A. H., 2001. Role of serine/threonine protein phosphatase 2A in cancer. Cancer Letter, 10(170), pp. 1-13. Sents, W. et al., 2013. The biogenesis of active protein phosphatase 2A holoenzymes: a tightly regulated process creating phosphatase specificity. FEBS Journal, Volume 280, p. 644–661. Seshacharyulu, P., Pandey, P., Datta, K. & Batra, S. K., 2013. Phosphatase: PP2A structural importance, regulation and its aberrant expression in cancer. Cancer Letter, 10(335), pp. 9-18. Sharma, N. K., 2010. Molecular Docking: An overview. Journal of Advanced Scientific Research, 1(1), pp. 62-72. Silverstein, A. M., Barrow, C. A., Davis, A. J. & Mumby, M. C., 2002. Actions of PP2A on the MAP kinase pathway and apoptosis are mediated by distinct regulatory subunits. PNAS, 99(7), p. 4221– 4226. Sontag, E., 2009. Role of PP2A methylation pathways in tau regulation. Alzheimers & Dementia, 5(4), pp. P94-P102. Sontag, J. et al., 2010. Regulation of Protein Phosphatase 2A methylation and PME-1 Play a critical role in differentiation of neuroblastoma cells. Journal of Neurochemistry, 11(5), pp. 1455-1465. Stanevich, V. et al., 2011. The structural basis for tight control of PP2A methylation and function by LCMT-1. Molecular Cell, 41(3), pp. 331-342. Sussman, J. et al., 1999. The protein data bank. Genetica, 106(1), pp. 149-158. Tamanoi, F. & Clarke, S. G., 2006. The Enzymes: Protein Methyltransferases. Burlington, MA: Academic Press. Taylor, R. D., Jewsbury, P. J. & Essex, J. W., 2002. A review of protein-small molecule docking methods.. Journal of Computer Aided Molecular Design, 16(3), pp. 151-166. Teodoro, M. L., Phillips, G. N. & Kavraki, L. E., 2010. Molecular Docking: A Problem With Thousands Of Degrees Of Freedom. Biochemistry and Cell Biology, pp. 1-7. Thiriet, M., 2011. Cell and Tissue Organization in the Circulatory and Ventilatory Systems. New York: Springer. Tramontano, A., 2007. Introduction to Bioinformatics. 1 ed. Danvers MA: CRC Press. Westbrook, J. et al., 2003. The Protein Data Bank and structural genomics. Nucleic acids research, 3(1), pp. 489-491. Read More