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Title
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Crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MgATP and peptide inhibitor.
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Authors
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J.Zheng,
D.R.Knighton,
L.F.ten Eyck,
R.Karlsson,
N.Xuong,
S.S.Taylor,
J.M.Sowadski.
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Ref.
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Biochemistry, 1993,
32,
2154-2161.
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PubMed id
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Abstract
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The structure of a ternary complex of the catalytic subunit of cAMP-dependent
protein kinase, MgATP, and a 20-residue inhibitor peptide was determined at a
resolution of 2.7 A using the difference Fourier technique starting from the
model of the binary complex (Knighton et al., 1991a). The model of the ternary
complex was refined using both X-PLOR and TNT to an R factor of 0.212 and 0.224,
respectively. The orientation of the nucleotide and the interactions of MgATP
with numerous conserved residues at the active site of the enzyme are clearly
defined. The unique protein kinase nucleotide binding site consists of a
five-stranded antiparallel beta-sheet with the base buried in a hydrophobic site
along beta-strands 1 and 2 and fixed by hydrogen bonds to the N6 amino and N7
nitrogens. The small lobe secures the nucleotide via a glycine-rich loop and by
ion pairing with Lys72 and Glu91. While the small lobe fixes the nontransferable
alpha- and beta-phosphates in this inhibitor complex, the gamma-phosphate is
secured by two Mg2+ ions and interacts both directly and indirectly with several
residues in the large lobe--Asp184, Asn171, Lys168. Asp166 is positioned to
serve as a catalytic base. The structure is correlated with previous chemical
evidence, and the features that distinguish this nucleotide binding motif from
other nucleotide binding proteins are delineated.
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