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PDBsum entry 1wbc
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Serine protease inhibitor
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PDB id
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1wbc
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References listed in PDB file
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Key reference
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Title
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Structure of a kunitz-Type chymotrypsin from winged bean seeds at 2.95 a resolution.
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Authors
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J.K.Dattagupta,
A.Podder,
C.Chakrabarti,
U.Sen,
S.K.Dutta,
M.Singh.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 1996,
52,
521-528.
[DOI no: ]
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PubMed id
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Abstract
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Thc crystal structure of an alpha-chymotrypsin inhibitor (P6(1)22; a = 61.4, c =
210.9 A) isolated from winged bean (Psophocarpus. tetragonolobus) seeds has been
determined at 2.95 A resolution by the molecular-replacement method using the
2.6 A coordinates of Erythrina trypsin inhibitor (ETI) as the starting model
(57% sequence homology). This protease inhibitor, WCI, belongs to the Kunitz
(STI) family and is a single polypeptide chain with 183 amino-acid residues
having a molecular weight of 20 244 Da. Structure refinement with RESTRAIN and
X-PLOR has led to a crystallographic R factor of 19.1% for 3469 observed
reflections (I > 2sigma) in the resolution range 8-2.95 A. A total of 56 water
molecules have been incorporated in the refined model containing 181 amino-acid
residues. In the refined structure the deviations of bond lengths and bond
angles from ideal values are 0.015 A and 2.2 degrees, respectively. The
inhibitor molecule is spherical and consists of 12 antiparallel beta-strands
with connecting loops arranged in a characteristic folding (a six-stranded
beta-barrel and a six-stranded lid on one hollow end of the barrel) common to
other homologous serine protease inhibitors in the Kunitz (STI) family as well
as to some non-homologous proteins like interleukin-lalpha and
interleukin-lbeta. In the structure the conformation of the protruding
reactive-site loop is stabilized through hydrogen bonds mainly formed by the
side chain of Asnl4, which intrudes inside the cavity of the reactive-site loop,
with the side-chain and main-chain atoms of some residues in the loop region. A
pseudo threefold axis exists parallel to the barrel axis of the structure. Each
of the three subdomains comprises of four beta-strands with connecting loops.
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Figure 5.
Fig. 5. The hydrophobic core of the
/3-barrel seen down the barrel
axis.
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Figure 6.
Fig. 6. Hydrogen bonding (indicated
by lines) in the reactive-
site loop. water O atom is
indicated by a dark
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(1996,
52,
521-528)
copyright 1996.
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