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Figure 5.
Figure 5 Comparison of ATP-binding sites in different
kinases. a, Comparison of the structure of p19^INK4d/Cdk6 with
those of Cdk2 (ref. 15) and Cdk2 from the cyclin A complex16,17.
Cdk6 was superimposed on Cdk2 (r.m.s. deviation was 0.56 ? over
70 residues) and Cdk2 from the cyclin A complex (r.m.s.
deviation was 0.49 ? over 70 residues) by aligning the C  atoms
in the -helices
in the C-terminal domain of both proteins. Loop L5 and the
linker (loop L7) (Fig. 3c), which anchor the N- and C-terminal
domains together, are labelled. b, The same structures, showing
only the N-terminal domain, illustrating the changes in position
of the N-terminal  -sheet
and helix 1.
In both a and b, the N-terminal domains and T-loop are coloured
red (Cdk2), yellow (Cdk2 from the cyclin A complex) and blue
(Cdk6); other regions of all three proteins are coloured grey.
In b, helices 3
and 5
of cyclin A, which interact with PSTAIRE helix 1
in cyclin A/Cdk2 (refs 16, 17), are green. c, The ATP-binding
site in Cdk6. Lys 29, His 100 and Asp 102, which together might
inhibit ATP binding, are labelled, as are key active-site
residues and the phosphate-binding loop L2. ATP, from the active
Cdk2/cyclin A complex17, is superimposed on the structure with
the N1 and N6 adenine nitrogens making conserved hydrogen bonds
with the carbonyl of Glu 99 and amide of Val 101,
respectively17,34. The structures of Cdk6 and ATP are yellow and
green, respectively. Carbon, nitrogen, oxygen and phosphorus
atoms are yellow, blue, red and yellow, respectively. The
structure of Cdk2 from the cyclin A/Cdk2 complex17 is blue.
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