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/* Structure-Activity Relationships(SARs) */
[[Image:5-alpha-reductase inhibition.jpeg]]
==== StructureGSK-Activity Relationships(SARs) 3 Inhibition====* ''GSK-3 inhibition targets treatment of chemotherapy-induced alopecia''[[Imagehttp:SAR_map//www.gif]biomedcentral.com/1471-2199/5/15 source]* In the canonical Wnt signaling cascade, adenomatous polyposis coli (APC), axin, and GSK3 constitute the so-called destruction complex, which controls the stability of beta-catenin. It is generally believed that four conserved Ser/Thr residues in the N terminus of beta-catenin are the pivotal targets for the constitutively active serine kinase GSK3. GSK3 covalently modifies beta-catenin by attaching phosphate groups (from ATP) to serine, and threonine residues. In so doing, the functional properties of the protein kinase’s substrate (beta-catenin) are modified.
* In the absence of Wnt signals, glycogen synthase kinase (GSK) is presumed to phosphorylate the N-terminal end of beta-catenin, thus promote degradation of beta-catenin and subsequent ubiquitination and proteasomal targeting.
* Exposure of cells to Wnts leads to inactivation of GSK-3 through an as yet unclear mechanism.The phosphoprotein Dishevelled is required, after receptor-ligand interaction, to transduce the signal that results in the inactivation of GSK-3. As a result, beta-catenin is dephosphorylated and escapes the ubiqduitylation-dependent destruction machinery.
* Unphosphorylated beta-catanin accumulates in the cytoplasm and translocates to the nucleus, where it can associate with the TCF/LEFs and become a transcriptional transactivator.
'''[[More details on GSK-3]]'''
'''Key points'''
* Beta-catenin phosphorylation at serine 45 (Ser45), threonine 41 (Thr41), Ser37, and Ser33 is critical for beta-catenin degradation. [http://jb.oxfordjournals.org/cgi/content/abstract/132/5/697 source]
* Regulation of beta-catenin phosphorylation is a central part of the canonical Wnt signaling pathway. [http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ProduktNr=223838&ArtikelNr=66755&filename=66755.pdf source]
* Ser-X-X-X-Ser (X is any amino acid) motif is obligatory for beta-catenin phosphorylation by GSK3.[http://lib.bioinfo.pl/auth:He,X source]
* Beta-catenin phosphorylation/degradation and its regulation by Wnt can occur normally in the absence of Thr41 as long as the Ser-X-X-X-Ser motif/spacing is preserved. [httSp://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/2006/45/i16/abs/bi0601149.html source]
'''GK3 Inhibition:'''
* GSK3 is regulated by phosphorylation.
* Phosphorylation of GSK3beta on Ser9 (Ser21 in GSK3alpha) by protein kinase B (PKB) causes its inactivation is the primary mechanism responsible for growth factor inhibition of this kinase. Activation of GSK3beta is dependent upon the phosphorylation of Tyr216 (Tyr279 in GSK3alpha). Upon activation, it has been shown to phosphorylate a number of different cellular proteins, including p53, c-Myc, c-Jun, heat shock factor-1 (HSF-1), beta-catenin and cyclin D1. [http://www.bioreagents.com/index.cfm/fuseaction/products.detail/CatNbr/OPA1-03082 source]
* GSK3 is inhibited by phosphorylation of serine-9 or serine-21 in GSK3beta and GSK3alpha, respectively. [http://lib.bioinfo.pl/auth:Friedman,AB source]
* GSK3’s substrate specificity is unique in that phosphorylation of substrate only occurs if a phosphoserine or phosphotyrosine is present four residues C-terminal to the site of GSK phosphorylation. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11430833&dopt=Abstract source]
* A phosphorylation cascade starts from GSK3 itself and initiates it in beta-catenin. [http://www.genesdev.org/cgi/content/full/16/16/2073 source]
* Thus our goal is to stop the phosphorylation of the serine and threonine residue of GSK3.
* The figure below illustrates the phosphorylation mechanism of serine and threonine by ATP.
[[image:GSK3_phosphorylation.jpg|400 px|center|thumb|Phosphorylation mechanism [http://images.google.com/images?q=tbn:DGnhgZ7y7pSejM:bass.bio.uci.edu/~hudel/bs99a/lecture26/phosphoaa.gif source]]]
* We can't stop conversion of ADP to ATP that relaseas Phosphorous group causing Phosphorylation.
* We can only block the oxygen atom on serine and threonine as a result which will in turn stop Phosphorylation.
* The two probable ways of blocking the oxygen atom are (a) As oxygen is a Lewis acid with strong electron donating capacity, so usually a strong electron pair acceptor can easily bind to oxygen atom and preventing phosphorylation or (b) breaking of the -OH bond with the carbon atom.
'''Serine - pyrazole reaction'''
[[image:serine-pyrazol.jpg|600 px|center|thumb|Serine and Pyrazole reaction [http://www.genome.ad.jp/dbget-bin/www_bget?rn+R03134 source]]]
* The T-loop of GSK-3 is tyrosine phosphorylated at Y216 and Y279 in GSK-3b and GSK-3a, respectively, but not threonine phosphorylated. Y216/Y279 phosphorylation could play a role in forcing open the substrate (e.g, beta-catanin)-binding site.
* Thus, T-loop tyrosine might facilitate substrate phosphorylation but is not strictly required for kinase activity.
* Stimulation of cells with pyrazole compounds cause inactivation of GSK-3 through phosphorylation (S9 of GSK-3 beta and S21 of GSK-3 alpha), which inhibits GSK-3 activity. Thus leading to dephosphorylation of substrates (e.g., beta-catanin) resulting in their functional activation and consequent increased hair follicle morphogenisis.
* Phosphorylation of S9/S21 creates a primed pesudosubstrate that binds intramolecularly to the positively charged pocket of the GSK-3. This folding precludes phosphorylation of substrates (eg., beta-catanin) because the catalytic groove is occupied. The mechanism of inhibition is competitive.
* A consequence of this is that primed substrates, in high enough concentrations, out-compete the pesudosubstrate and thus become phosphorylated.
* Thus, small molecule inhibitors modeled to fit in the positively charged pocket of the GSK-3 kinease domain could potentially be very effective for selective inhibition of primed substrates.
'''Proposed mechanisms to regulate GSK-3''' [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Abstract&list_uids=12615961 source]
# inactivation of GSK-3 through serine phosphorylation
# activation of GSK-3 through tyrosine phosphorylation
# inactivation of GSK-3 through tyrosine dephosphorylation
# Covalant modifications of substrates through priming phosphorylation
# inhibition or facilation of GSK-3 mediated substrate phosphorylation thriugh interation of GSK-3 with binding or scaffolding proteins
# targeting of GSK-3 to different subcellular localizations
# differential usage of isoforms or splice variants to alter subcellular localization or substrate specificity
# integration of parellel signals conveyed by a signal stimulus.
'''Key Finding'''
* '''Pyrazole compounds with inhibition constant (Ki) of <0.1 mM''' are a good starting point for developing molecules that can inhibit serine/threonine protein kinase (such as GSK-3) and the proteins they help to regulate. [http://www.chemistry.org/portal/a/c/s/1/acsdisplay.html?DOC=patentwatch%5Carchive%5C011204_patentwatch.html source]
==== Structure-Activity Relationships(SARs) ====
[[Image:SAR_map.gif]]
== Questions Dolcera Answers ==
