Differences in substrate specificity between Cdk2-cyclin A and Cdk2-cyclin E in vitro.

Cyclin-dependent kinase 2 (Cdk2), when bound to either cyclin A or cyclin E, recognizes the Ser/Thr-Pro-X-basic amino acid (motif A) as a phosphorylation site. In this study, we designed several peptides based on motif A and examined the substrate specificity of Cdk2-cyclin A and Cdk2-cyclin E using these peptides. Peptides containing a proline residue in the sequence Pro-X-Thr-Pro-X-basic amino acid (motif B) had higher affinity for both Cdk2 complexes than peptides containing motif A. Furthermore, differences in substrate affinity between the two Cdk2 complexes were caused by a proline residue adjacent to or three positions before the threonine residue. Similarly, the presence of different basic amino acids in motif B also had different effects on affinity for each complex. We demonstrate the possibility that the substrate specificity of Cdk2 bound to cyclin might be regulated by the species of cyclin.