CDKN1B - Biochemical Function

Biochemical Function

The p27Kip1 gene has a DNA sequence similar to other members of the "Cip/Kip" family which include the p21Cip1/Waf1 and p57Kip2 genes. In addition to this structural similarity the "Cip/Kip" proteins share the functional characteristic of being able to bind several different classes of Cyclin and Cdk molecules. For example, p27Kip1 binds to cyclin D either alone, or when complexed to its catalytic subunit CDK4. In doing so p27Kip1 inhibits the catalytic activity of Cdk4, which means that it prevents Cdk4 from adding phosphate residues to its principal substrate, the retinoblastoma (pRb) protein. Increased levels of the p27Kip1 protein typically cause cells to arrest in the G1 phase of the cell cycle. Likewise, p27Kip1 is able to bind other Cdk proteins when complexed to cyclin subunits such as Cyclin E/Cdk2 and Cyclin A/Cdk2.