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OCA, Dimitri Feltrin

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 == '''Introduction'''==
-Cyclin dependent kinasaes (CDKs) are a family of serine/threonine kinases, which are responsible for cell cycle progression. They are regulated by several upstream pathways, such as the CDK activating kinase and interaction with Cyclin D <ref> PMID: 16782892 </ref><ref> PMID: 8139570 </ref>. After association of CDK with cyclin and the active CKK/cyclin complex phosphorylates and herefore inactivates retinoblastoma protein family members. This leads to activation of E2F target genes. One of these genes is cyclin E which triggers G1 phase cell cycle progression.<br />
+Cyclin dependent kinasaes (CDKs) are a family of serine/threonine kinases, which are responsible for cell cycle progression. They are regulated by several upstream pathways, such as the CDK activating kinase and interaction with Cyclin D. After association of CDK with cyclin, the active CDK/cyclin complex phosphorylates and herefore inactivates [http://www.proteopedia.org/wiki/index.php/Retinoblastoma_protein retinoblastoma] protein family members. This leads to activation of E2F target genes. One of these genes is cyclin E which triggers G1 phase cell cycle progression.<br />
-CDKs and cyclins are particularly interesting because a dysfunction of their pathways are associated to numerous cancers <ref> PMID: 11960696 </ref><ref> PMID: 12204530  </ref><ref> PMID: 11902577 </ref>. Among all genetic alterations of CDK/cyclin in cancer that one of CDK4 and cyclin D1 is most common. Appearance of breast cancer goes normally hand in hand with increased cyclin D1 levels, caused by genetic amplification or overexpression <ref> PMID: 15961768 </ref>. In liposarcomas the CDK4 gene is amplified <ref> PMID: 16160477 </ref>.  Cyclin D1 translocations play also a role in mantle cell lymphoma and multiple myelomas <ref> PMID: 12683869 </ref><ref> PMID: 15090460 </ref>. Furthermore mutations of CDK4, which alter its structure in a manner that it becomes unable to bind regulative tumor supressor ptoeins result in defective CDK4 repression and therefore dysregulate the cell cylce <ref> PMID: 7652577 </ref>. It becomes obvious that cyclin D1 CDK4 interaction is critical for the development of several cancers. Therefore CDKs, in particular CDK4 are a promising target of novel cancer drugs <ref> PMID: 16584130 </ref>.
+CDKs and cyclins are particularly interesting because a dysfunction of their pathways are associated to numerous cancers. Among all genetic alterations of CDK/cyclin in cancer that one of CDK4 and cyclin D1 is most common. Appearance of breast cancer goes normally hand in hand with increased cyclin D1 levels, caused by genetic amplification or overexpression <ref> PMID: 15961768 </ref>. In liposarcomas the CDK4 gene is amplified <ref> PMID: 16160477 </ref>.  Cyclin D1 translocations play also a role in mantle cell lymphoma and multiple myelomas <ref> PMID: 12683869 </ref>. Furthermore mutations of CDK4, which alter its structure in a manner that it becomes unable to bind regulative tumor supressor proteins result in defective CDK4 repression and therefore dysregulate the cell cylce. It becomes obvious that cyclin D1 CDK4 interaction is critical for the development of several cancers. Therefore CDKs, in particular CDK4 are a promising target of novel cancer drugs.
 == '''CDK4 structure''' ==
-In order to gain structural information about CDKs a crystallography analysis of CKD in complex with cylcin D was performed. CDK4 and cylcin D1, were over expressed in insect cells for crystallisation and slightly modified for better crystallization. CDK 4 possesses the typical bilobal structure of kinases, containing a 5-strandet ß-sheet and a N-terminal domain (residues 1-96). Within the N-terminal domain the helix alpha-C is packed against the ß-sheet. Furthermore an ATP binding site is located in between these domains, which might bind ATP after minimal conformational rearrangement of residues Asp-99, Asp-140, Lys-142, and Tyr-17. Residues 161-171 form a T-loop containing alpha-helices. Phosphorylation of this T-loop or cylcin D binding may change its conformation in order to activate kinase activity of CDK4. Lambda-phosphatase incubation stustudies confirm the importance of phosphorylation of the T-loop for full kinase activity <ref> PMID: 19237565 </ref>.
+In order to gain structural information about CDKs, a crystallographic analysis of CDK in complex with cyclin D was performed. CDK4 and cyclin D1, were overexpressed in insect cells for crystallisation and slightly modified for better crystallization. CDK 4 possesses the typical bilobal structure of kinases, containing a 5-strandet ß-sheet and a N-terminal domain (residues 1-96). Within the N-terminal domain the helix alpha-C is packed against the ß-sheet. Furthermore an ATP binding site is located in between these domains, which might bind ATP after minimal conformational rearrangement of residues Asp-99, Asp-140, Lys-142, and Tyr-17. Residues 161-171 form a T-loop containing alpha-helices. Phosphorylation of this T-loop or cyclin D binding may change its conformation in order to activate kinase activity of CDK4. Lambda-phosphatase incubation studies confirm the importance of phosphorylation of the T-loop for full kinase activity <ref> PMID: 19237565 </ref>.
 == '''Cyclin D1 structure''' ==
-Cyclin D1 consists of a double glycin box domain fold, containing 11 alpha helices. Its secondary structure is generally equivalent to the structure of other cylcins. Furthermore is contains 2 Rb binding sites comprising an LxCxE motive t its N-terminal site. Structural conservation of the RxL motive, responsible for peptide binding was observed on Cyclin D1 and Cyclin A. Peptide binding studies substantiate this observation <ref> PMID: 19237565 </ref>.
+Cyclin D1 consists of a double glycin box domain fold, containing 11 alpha helices. Its secondary structure is generally equivalent to the structure of other cyclins. Furthermore, it contains 2 Rb binding sites comprising an LxCxE motive t its N-terminal site. Structural conservation of the RxL motive, responsible for peptide binding was observed on Cyclin D1 and Cyclin A. Peptide binding studies substantiate this observation <ref> PMID: 19237565 </ref>.
 == '''Cyclin D1-CDK4 complex''' ==
-CDK4 in complex with Cyclin D1 shows an engagement of the CDK4 alpha-helix with cylcin D1. Nevertheless the helix does perform the conformational switch, normally known for CDK activation in other CDK/cyclin complexes <ref> PMID: 7630397 </ref>. Surprisingly the CDK4/cyclin D1 structure reminds to the structures of inactive structures of non cyclin bound CDK2 and CDK7 <ref> PMID: 8510751 </ref><ref> PMID: 15530371 </ref>. Further stabilization of the CDK4 T-loop in the inactive confirmation is achieved by interactions of C- and N- terminal lobes of the kinase. These residues, containing an Asp158–Phe–Gly160 (DFG) motif are condensed into a helix, which is stabilized by interactions with the alpha-C-helix, ß4-strand, ß6-strand as well as the apex of the T-loop. The architecture of the T-Loop is similar to the one observed at CDK7 and CDK6. CDK4 kinase activation could be achieved due to movement of the alpha-C-helix. Although the C-alpha-lobe of CDK4 seems to be bound by Cylcin D1, the rotation of the C-lobe of CDK4 is not maximal. This reduces the buried surface area of of the CDK4/cyclin D1 interface in comparison of the buried surface of other CDK/cyclin complexes <ref> PMID: 19237565 </ref>.
+CDK4 in complex with Cyclin D1 shows an engagement of the CDK4 alpha-helix with cyclin D1. Nevertheless, the helix does perform the conformational switch, normally known for CDK activation in other CDK/cyclin complexes <ref> PMID: 7630397 </ref>. Surprisingly, the CDK4/cyclin D1 structure reminds to the structures of inactive structures of non cyclin bound CDK2 and CDK7 <ref> PMID: 8510751 </ref>. Further stabilization of the CDK4 T-loop in the inactive confirmation is achieved by interactions of C- and N- terminal lobes of the kinase. These residues, containing an Asp158–Phe–Gly160 (DFG) motif are condensed into a helix, which is stabilized by interactions with the alpha-C-helix, ß4-strand, ß6-strand as well as the apex of the T-loop. The architecture of the T-Loop is similar to the one observed at CDK7 and CDK6. CDK4 kinase activation could be achieved due to movement of the alpha-C-helix. Although the C-alpha-lobe of CDK4 seems to be bound by Cyclin D1, the rotation of the C-lobe of CDK4 is not maximal. This reduces the buried surface area of of the CDK4/cyclin D1 interface in comparison of the buried surface of other CDK/cyclin complexes.
 == '''CDK4 in its biological context''' ==