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Title
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Recognition between a bacterial ribonuclease, barnase, and its natural inhibitor, barstar.
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Authors
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V.Guillet,
A.Lapthorn,
R.W.Hartley,
Y.Mauguen.
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Ref.
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Structure, 1993,
1,
165-176.
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PubMed id
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Abstract
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BACKGROUND: Protein-protein recognition is fundamental to most biological
processes. The information we have so far on the interfaces between proteins
comes largely from several protease-inhibitor and antigen-antibody complexes.
Barnase, a bacterial ribonuclease, and barstar, its natural inhibitor, form a
tight complex which provides a good model for the study and design of
protein-protein non-covalent interactions. RESULTS: Here we report the structure
of a complex between barnase and a fully functional mutant of barstar determined
by X-ray analysis. Barstar is composed of three parallel alpha-helices stacked
against a three-stranded parallel, beta-sheet, and sterically blocks the active
site of the enzyme with an alpha-helix and adjacent loop. The buried surface in
the interface between the two molecules totals 1630 A2. The barnase-barstar
complex is predominantly stabilized by charge interactions involving positive
charges in the active site of the enzyme. Asp39 of barstar binds to the
phosphate-binding site of barnase, mimicking enzyme-substrate interactions.
CONCLUSION: The phosphate-binding site of the enzyme is the anchor point for
inhibitor binding. We propose that this is also likely to be the case for other
ribonuclease inhibitors.
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