The structural basis for control by phosphorylation

The talk will review our current understanding of the structural consequences of post translational modification by phosphorylation. Studies on active and inactive protein kinases have taught us much about the role of the activation segment in control of kinase activity. We have recently solved the structure of the active phosphorylase kinase catalytic domain in complex with a peptide substrate. The peptide sequence was derived from sequences obtained from the peptide library search for kinase specilicities by Cantley and colleagues. The results demonstrate a key role for the activation segment in substrate recognition that is likely to be common for many protein kinases. Studies with the cyclin dependent protein kinase, CDK2, and its phosphorylation by Civl (CAK in vivo), the kinase activating enzyme from S. cerevisiae, have shown that phosphorylalion of CDK2 proceeds more rapidly with CDK2 alone than in the presence of cyclin A. The activity of the phosphorylated CDK2 is ().39f of the fully active CDK2(phosphorylated)-cyclin A complex. The crystal structure of the phosphorylated CDK2 shows an inactive conformation in which the activation segment not localised. The structural results provide an explanation for the low activity, Staurosporine is a potent inhibitor for most but not all protein kinases. Recent structural studies with CDK2-staurosporine complex have shown the structural basis for the potent inhibition of CDK2 and provide possible explanations for lower potency against certain protein kinases such asCDK4 and CKl.