"Our goal was to obtain structural information about any cyclin-CDK complex
," says Nikola P.
The CIP/KIP proteins have broad specificity as compared to INK4 proteins for binding and inhibiting the cyclin-CDK complexes
. The activity of cyclin-D-CDK4 is inhibited by these proteins, preventing the Rb phosphorylation during the transition of G1 to S phase and inhibit the activity of cyclin-A-CDK2 and cyclin-E-CDK2 in late G1 and early S phase respectively (Sharpless, 2005).
Both SI and RRI function on the suppression of p53 and its target p21; the latter serves as an inhibitor of G1/S cyclin-CDK complexes
[9, 10, 21].
Functional inactivation of the retinoblastoma protein requires sequential modification by at least two distinct cyclin-cdk complexes
Activation of cyclin-CDK complexes
plays a central role in cell cycle progression and arrest processes [22,23].
It binds to cyclin-CDK complexes
to inhibit their catalytic activity and induce cell-cycle arrest (Coqueret 2003: Fukuchi et al.
It can stop the cell at any point because it inhibits all of the cyclin-CDK complexes
that nudge the cell through these various stages of division.
Another mechanism that prevents premature entry into the S phase relies on CDK inhibitors (CKIs) that bind onto cyclin-CDK complexes
and disrupt their catalytic centre (Pavletich 1999).