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Title
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Crystal structure of a cyclic AMP-independent mutant of catabolite gene activator protein.
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Authors
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I.T.Weber,
G.L.Gilliland,
J.G.Harman,
A.Peterkofsky.
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Ref.
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J Biol Chem, 1987,
262,
5630-5636.
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PubMed id
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Abstract
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Escherichia coli NCR91 synthesizes a mutant form of catabolite gene activator
protein (CAP) in which alanine 144 is replaced by threonine. This mutant, which
also lacks adenylate cyclase activity, has a CAP phenotype; in the absence of
cAMP it is able to express genes that normally require cAMP. CAP91 has been
purified and crystallized with cAMP under the same conditions as used to
crystallize the wild type CAP X cAMP complex. X-ray diffraction data were
measured to 2.4-A resolution and the CAP91 structure was determined using
initial model phases from the wild type structure. A difference Fourier map
calculated between CAP91 and wild type showed the 2 alanine to threonine
sequence changes in the dimer and also a change in orientation of cysteine 178
in one of the subunits. The CAP91 coordinates were refined by restrained least
squares to an R factor of 0.186. Differences in the atomic positions of the wild
type and mutant protein structures were analyzed by a vector averaging
technique. There were small changes that included concerted motions in the small
domains, in the hinge between the two domains and in an adjacent loop between
beta-strands 4 and 5. The mutation at residue 144 apparently causes changes in
the position of some protein atoms that are distal to the mutation site.
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