Subdomain II of Cyclin-Dependent Kinase 2
Subdomain II includes residues 26-43, which comprises the beta-3 strand
of the small lobe. Beta-3 is found between loop regions 3 and 4. Cdk2 does not
have the alpha-helix seen in subdomain II in some of the other protein
kinase structures, such as PKA. The conserved lysine needed for maximum
enzyme function is at position 33 in beta-3 of the small lobe. In cAPK, this
lysine functions in anchorage and orientation of the ATP and it forms a
salt bridge with the carboxyl group of the conserved Glu91 in subdomain
III. In Cdk2, this does not occur because the presense of the alpha-L12 helix,
which is not present in cAPK, increases the distance between Lys33 and Glu51.
cAPK instead has a beta-strand.
In mutation experiments, it was found that the residues Arg36,
Asp38, Glu40, and Glu42 of subdomain II must be intact in order for cyclin to