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PDBsum entry 2ody
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Blood clotting/blood clotting inhibitor
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PDB id
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2ody
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Contents |
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44 a.a.
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255 a.a.
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40 a.a.
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127 a.a.
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References listed in PDB file
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Key reference
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Title
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Isolation, Cloning and structural characterisation of boophilin, A multifunctional kunitz-Type proteinase inhibitor from the cattle tick.
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Authors
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S.Macedo-Ribeiro,
C.Almeida,
B.M.Calisto,
T.Friedrich,
R.Mentele,
J.Stürzebecher,
P.Fuentes-Prior,
P.J.Pereira.
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Ref.
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Plos One, 2008,
3,
e1624.
[DOI no: ]
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PubMed id
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Abstract
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Inhibitors of coagulation factors from blood-feeding animals display a wide
variety of structural motifs and inhibition mechanisms. We have isolated a novel
inhibitor from the cattle tick Boophilus microplus, one of the most widespread
parasites of farm animals. The inhibitor, which we have termed boophilin, has
been cloned and overexpressed in Escherichia coli. Mature boophilin is composed
of two canonical Kunitz-type domains, and inhibits not only the major
procoagulant enzyme, thrombin, but in addition, and by contrast to all other
previously characterised natural thrombin inhibitors, significantly interferes
with the proteolytic activity of other serine proteinases such as trypsin and
plasmin. The crystal structure of the bovine alpha-thrombin.boophilin complex,
refined at 2.35 A resolution reveals a non-canonical binding mode to the
proteinase. The N-terminal region of the mature inhibitor, Q16-R17-N18, binds in
a parallel manner across the active site of the proteinase, with the guanidinium
group of R17 anchored in the S(1) pocket, while the C-terminal Kunitz domain is
negatively charged and docks into the basic exosite I of thrombin. This binding
mode resembles the previously characterised thrombin inhibitor, ornithodorin
which, unlike boophilin, is composed of two distorted Kunitz modules.
Unexpectedly, both boophilin domains adopt markedly different orientations when
compared to those of ornithodorin, in its complex with thrombin. The N-terminal
boophilin domain rotates 9 degrees and is displaced by 6 A, while the C-terminal
domain rotates almost 6 degrees accompanied by a 3 A displacement. The
reactive-site loop of the N-terminal Kunitz domain of boophilin with its P(1)
residue, K31, is fully solvent exposed and could thus bind a second trypsin-like
proteinase without sterical restraints. This finding explains the formation of a
ternary thrombin.boophilin.trypsin complex, and suggests a mechanism for
prothrombinase inhibition in vivo.
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