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Title
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Structural basis for the inactivation of the P54 mutant of beta-lactamase from Staphylococcus aureus PC1.
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Authors
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O.Herzberg,
G.Kapadia,
B.Blanco,
T.S.Smith,
A.Coulson.
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Ref.
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Biochemistry, 1991,
30,
9503-9509.
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PubMed id
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Abstract
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The crystal structure of a mutant protein of a class A beta-lactamase from
Staphylococcus aureus PC1, in which Asp179 is replaced by an asparagine (P54),
has been determined and refined at 2.3-A resolution (1 A = 0.1 nm). The
resulting crystallographic R factor [formula: see text] are the observed and
calculated structure factor amplitudes) is 0.181 for 12289 reflections with I
greater than or equal to sigma (I) within the 6.0-2.3-A resolution range. The
mutated residue is located at the C-terminus of an extensive loop (the
omega-loop), remote from the active site, and results in a drastically reduced
activity. Examination of the native and P54 structures reveals that the overall
fold is similar, except that there is substantial disorder of the omega-loop of
P54. This is a consequence of the elimination of a salt bridge between Asp179
and Arg164 that links the two ends of the omega-loop in native beta-lactamase.
It is associated with a difference in side-chain conformation between Asn179 in
P54 and Asp179 in the native structure. An alternate interaction occurs in P54
between Asn179 and Ala69, adjacent to the catalytic Ser70. This disorder affects
catalysis since some of the disordered residues, in particular Glu166, form part
of the active site.(ABSTRACT TRUNCATED AT 250 WORDS)
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