Two large classes of GTPase switch proteins are used in signal transduction pathways:

1. Heterotrimeric G proteins

2. Monomeric G proteins

TLS Online TPP Program

#Id: 8609

#XL - T Zoology

In free CDK2, the A-loop blocks access of protein substrates to the γ phosphate of the bound ATP.

TLS Online TPP Program

#Id: 8610

#XL - T Zoology

TLS Online TPP Program

#Id: 8611

#XL - T Zoology

Nonphosphorylated CDK bound to one of its cyclin partners has minimal but detectable protein kinase activity in vitro, although it may be essentially inactive in vivo.

TLS Online TPP Program

#Id: 8612

#XL - T Zoology

Phosphorylation of a critical threonine residue in the activation loop, Thr-160, allowing substrates to access the active site of the CDK

TLS Online TPP Program

#Id: 8613

#XL - T Zoology

Threonine -160 phosphorylation is mediated by 

CDK-activating kinase (CAK)

TLS Online TPP Program

#Id: 8614

#XL - T Zoology

Two inhibitory phosphorylations on CDK play a critical role in controlling CDK activity:

Y15

T14