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PDBsum entry 1ay6
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Hydrolase/hydrolase inhibitor
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PDB id
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1ay6
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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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Molecular basis for the inhibition of human alpha-Thrombin by the macrocyclic peptide cyclotheonamide a.
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Authors
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B.E.Maryanoff,
X.Qiu,
K.P.Padmanabhan,
A.Tulinsky,
H.R.Almond,
P.Andrade-Gordon,
M.N.Greco,
J.A.Kauffman,
K.C.Nicolaou,
A.Liu.
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Ref.
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Proc Natl Acad Sci U S A, 1993,
90,
8048-8052.
[DOI no: ]
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PubMed id
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Abstract
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The macrocyclic peptide cyclotheonamide A (CtA), isolated from the marine sponge
Theonella sp., represents an unusual class of serine protease inhibitor. A
complex of this inhibitor with human alpha-thrombin, a protease central to the
bioregulation of thrombosis and hemostasis, was studied by x-ray
crystallography. This work (2.3-A resolution) confirms the structure of CtA and
reveals intimate details about its molecular recognition within the enzyme
active site. Interactions due to the "Pro-Arg motif" (Arg occupancy of
the S1 specificity pocket; formation of a hydrogen-bonded two-strand
antiparallel beta-sheet with Ser214-Gly216) and the alpha-keto amide group of
CtA are primarily responsible for binding to thrombin, with the alpha-keto amide
serving as a transition-state analogue. A special interaction with the
"insertion loop" of thrombin (Tyr60A-Thr60I) is manifested through
engagement of the hydroxyphenyl group of CtA with Trp60D as part of an
"aromatic stacking chain." Biochemical inhibition data (Ki values at
37 degrees C) were obtained for CtA with thrombin and a diverse collection of
serine proteases. Thus, CtA is just a moderate inhibitor of human alpha-thrombin
(Ki = 0.18 microM) but a potent inhibitor of trypsin (Ki = 0.023 microM) and
streptokinase (Ki = 0.035 microM). The relative lack of potency of CtA as a
thrombin inhibitor is discussed with respect to certain structural features of
the enzyme complex. We also report the total synthesis of CtA, by a convergent
fragment-condensation approach, to serve the preparation of
cyclotheonamide analogues for structure-function studies.
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