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Title
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The 2.5 A X-ray crystal structure of the acid-stable proteinase inhibitor from human mucous secretions analysed in its complex with bovine alpha-chymotrypsin.
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Authors
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M.G.Grütter,
G.Fendrich,
R.Huber,
W.Bode.
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Ref.
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Embo J, 1988,
7,
345-351.
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PubMed id
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Abstract
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Orthorhombic crystals of the complex formed between bovine alpha-chymotrypsin
and a recombinant human mucous proteinase inhibitor (SLPI) were grown. Data to
2.3 A resolution were collected on the area-detector diffractometer FAST. The
crystal structure of the complex was solved by Patterson search techniques using
chymotrypsin as a search model. A cyclic procedure of modeling and
crystallographic refinement enabled the determination of the SLPI structure. The
current crystallographic R-value is 0.19. SLPI has a boomerang-like shape with
both wings comprising two well separated domains of similar architecture. In
each domain the polypeptide chain is arranged like a stretched spiral. Two
internal strands form a regular beta-hairpin loop which is accompanied by two
external strands linked by the proteinase binding segment. The polypeptide
segment of each domain is interconnected by four disulfide bridges with a
connectivity pattern hitherto unobserved. The reactive site loop of the second
domain has elastase and chymotrypsin binding properties. It contains the
scissile peptide bond between Leu72I and Met73I and has a similar conformation
to that observed in other serine proteinase protein inhibitors. Eight residues
of this loop, two of the adjacent hairpin loop, the C-terminal segment and
Trp30I are in direct contact with the cognate enzyme. The binding loop of the
first domain (probably with anti-trypsin activity) is disordered due to
proteolytic cleavage occurring in the course of crystallization.
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