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Figure 1.
FIGURE 1. Overview of GRK1 and its active site. a,
GRK1[535]-His[6] crystallized as a homodimer using a conserved
interface of the RH domain in all the crystal forms. Shown is
the most complete structure, that of crystal form I. The RH
terminal subdomain is colored magenta (helices  0-3 and
8-11), and the bundle
subdomain (helices 4- 7) is slate blue. The
small lobe of the kinase domain (yellow) is composed of six
β-strands (orange) and two -helices ( B and
C),
whereas the large lobe is primarily -helical. The ligand
(Mg^2+)[2]·ATP is drawn as spheres. Magnesium atoms are
colored black, carbons are white, nitrogens are blue, oxygens
are red, phosphates are orange, and chloride ions are cyan. The
extreme N-terminal region and the C-terminal extension of the
kinase domain are green. b, substrate complex of GRK1. Shown is
a  [A]-weighted |F[o]| -
|F[c]| omit map contoured at 4 , wherein ATP, Mg^2+,
and associated waters (green) were excluded from refinement
(crystal form I and chain B). Lys^216 (β1 sheet, orange
carbons) coordinates the - and β-phosphates.
Glu^332 (yellow carbons) coordinates both Mg^2+ atoms. c,
product complex of GRK1. Shown is a [A]-weighted |F[o]| -
|F[c]| omit map contoured at 5 , wherein ADP, Mg^2+,
and associated waters were excluded from refinement (crystal
form IV). d, the peptide-binding channel of GRK1. The molecular
surface of GRK1 is colored by its electrostatic potential from
-7 (red, acidic) to +7 (blue, basic) kT/e^-. The channel has a
strikingly basic character, explaining why GRK1 prefers acidic
substrates (48, 49) and how it can phosphorylate multiple
closely spaced Ser and Thr residues at the C terminus of Rho^*.
The channel is also wider in GRK1 than in nucleotide-bound PKB
(e), reflecting the more open conformation of the GRK1 kinase
domain of GRK1. As a result, the phosphoacceptor oxygen of the
modeled peptide is >4 Å from the  -phosphate of ATP,
which is too far for covalent chemistry to occur. A model of
residues 332-345 from the C terminus of Rho^*, is shown as a
stick model docked to the large lobe with Ser^338 in position to
be phosphorylated (position "+0"). Residues in the F- G loop
of the large lobe appear to obstruct the N-terminal end of the
peptide-binding site. e, the GSK3β peptide bound to PKB. The
PKB kinase domain (Protein Data Bank code 1O6L [PDB]
) is in its closed conformation. The channel is markedly acidic,
in line with a preference for basic substrates.
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