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PDBsum entry 2stb
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Hydrolase/hydrolase inhibitor
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PDB id
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2stb
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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High-Resolution structures of three new trypsin-Squash-Inhibitor complexes: a detailed comparison with other trypsins and their complexes.
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Authors
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R.Helland,
G.I.Berglund,
J.Otlewski,
W.Apostoluk,
O.A.Andersen,
N.P.Willassen,
A.O.Smalås.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 1999,
55,
139-148.
[DOI no: ]
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PubMed id
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Abstract
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An anionic trypsin from Atlantic salmon and bovine trypsin have been complexed
with the squash-seed inhibitors, CMTI-I (Cucurbita maxima trypsin inhibitor I,
P1 Arg) and CPTI-II (Cucurbita pepo trypsin inhibitor II, P1 Lys). The crystal
structures of three such complexes have been determined to 1.5-1.8 A resolution
and refined to crystallographic R factors ranging from 17.6 to 19.3%. The two
anionic salmon-trypsin complexes (ST-CPTI and ST-CMTI) and the bovine-trypsin
complex (BT-CPTI) have been compared to other trypsin-inhibitor complexes by
means of general structure and primary and secondary binding features. In all
three new structures, the primary binding residue of the inhibitor binds to
trypsin in the classical manner, but with small differences in the primary and
secondary binding patterns. Lysine in CPTI-II binds deeper in the specificity
pocket of bovine trypsin than lysine in other known lysine-bovine-trypsin
complexes, and anionic salmon trypsin lacks some of the secondary binding
interactions found in the complexes formed between squash inhibitors and bovine
trypsin. The ST-CMTI complex was formed from the reactive-site-cleaved form of
the inhibitor. However, well defined electron density was observed for the
P1-P1' peptide bond, together with a hydrogen-bonding pattern virtually
identical to those of all serine-protease-protein-inhibitor complexes,
indicating a resynthesis of the scissile bond.
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Figure 1.
Figure 1 Electron density for residues at the N-terminus of
anionic salmon trypsin in complex with the squash-seed inhibitor
CPTI-II. The maps are from simulated annealing where residues 24
and 28 were refined as alanines. The 2F[o] - F[c] map (grey) is
contoured at 1.5  and
the F[o] - F[c] map (black) is contoured at 3 .
Both maps clearly identify residues 24 and 28 as prolines. The
coordinates of the final refined model are superimposed on the
simulated-annealing maps. The figure was produced using
BOBSCRIPT (Kraulis, 1991[Kraulis, P. J. (1991). J. Appl. Cryst.
24, 946-950.]; Esnouf, 1997[Esnouf, R. M. (1997). J. Mol. Graph.
15, 133-138.]).
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Figure 2.
Figure 2 Ribbon-style diagram of the complex between salmon
trypsin (red) and CPTI (blue). The P1 lysine residue of CPTI
penetrating the active site of trypsin is indicated along with
the structurally bound calcium ion (green) of trypsin.
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(1999,
55,
139-148)
copyright 1999.
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