Reversible protein phosphorylation serves as a key mechanism to regulate virtually every cellular process by altering the activation status, subcellular location, stability and/or protein-protein interactions of the target protein. Protein kinases, the enzymes that catalyze the phosphorylation reaction, are often themselves subject to phosphoregulation. Cyclin-dependent kinase 5 (CDK5) is a proline-directed serine/threonine kinase essential for embryonic development whose over-activation has been implicated in several pathologies including neuro-degeneration, cancer cell metastasis and type II diabetes. Therefore, it is important to investigate molecular mechanism(s) that mediate regulation of CDK5 activity. Here, we identify and characterize a novel phosphoregulatory site on CDK5. Our mass spectrometry analysis identified seven putative phosphorylation sites on CDK5. Using phosphomimetic and non-phosphorylatable mutants, we determined that phosphorylation of S47, one of the identified sites, renders the kinase catalytically inactive. The inactivation of the kinase due to the phosphomimetic change at S47 results from the inhibition of its interaction with its cognate activator, p35 as determined by co-immunoprecipitation assays. Finally, we connect the effect of this regulatory event to a cellular phenotype by showing that the S47D CDK5 mutant inhibits cell migration. Together, these results have uncovered a potential physiological mechanism to regulate CDK5 activity. The evolutionary conservation of this residue in not only CDK5, but also in other CDK family members suggests that this phosphosite may represent a shared regulatory mechanism across the CDK family.
|Commitee:||McAbee, Douglas, Schwans, Jason|
|School:||California State University, Long Beach|
|Department:||Chemistry and Biochemistry|
|School Location:||United States -- California|
|Source:||MAI 81/1(E), Masters Abstracts International|
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