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1rfn

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{{STRUCTURE_1rfn| PDB=1rfn | SCENE= }}
{{STRUCTURE_1rfn| PDB=1rfn | SCENE= }}
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'''HUMAN COAGULATION FACTOR IXA IN COMPLEX WITH P-AMINO BENZAMIDINE'''
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===HUMAN COAGULATION FACTOR IXA IN COMPLEX WITH P-AMINO BENZAMIDINE===
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==Overview==
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BACKGROUND: Among the S1 family of serine proteinases, the blood coagulation factor IXa (fIXa) is uniquely inefficient against synthetic peptide substrates. Mutagenesis studies show that a loop of residues at the S2-S4 substrate-binding cleft (the 99-loop) contributes to the low efficiency. The crystal structure of porcine fIXa in complex with the inhibitor D-Phe-Pro-Arg-chloromethylketone (PPACK) was unable to directly clarify the role of the 99-loop, as the doubly covalent inhibitor induced an active conformation of fIXa. RESULTS: The crystal structure of a recombinant two-domain construct of human fIXa in complex with p-aminobenzamidine shows that the Tyr99 sidechain adopts an atypical conformation in the absence of substrate interactions. In this conformation, the hydroxyl group occupies the volume corresponding to the mainchain of a canonically bound substrate P2 residue. To accommodate substrate binding, Tyr99 must adopt a higher energy conformation that creates the S2 pocket and restricts the S4 pocket, as in fIXa-PPACK. The energy cost may contribute significantly to the poor K(M) values of fIXa for chromogenic substrates. In homologs, such as factor Xa and tissue plasminogen activator, the different conformation of the 99-loop leaves Tyr99 in low-energy conformations in both bound and unbound states. CONCLUSIONS: Molecular recognition of substrates by fIXa seems to be determined by the action of the 99-loop on Tyr99. This is in contrast to other coagulation enzymes where, in general, the chemical nature of residue 99 determines molecular recognition in S2 and S3-S4. This dominant role on substrate interaction suggests that the 99-loop may be rearranged in the physiological fX activation complex of fIXa, fVIIIa, and fX.
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(as it appears on PubMed at http://www.pubmed.gov), where 10467148 is the PubMed ID number.
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{{ABSTRACT_PUBMED_10467148}}
==About this Structure==
==About this Structure==
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[[Category: Blood coagulation]]
[[Category: Blood coagulation]]
[[Category: Serine proteinase]]
[[Category: Serine proteinase]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 13:29:26 2008''

Revision as of 10:29, 28 July 2008

Image:1rfn.png

Template:STRUCTURE 1rfn

HUMAN COAGULATION FACTOR IXA IN COMPLEX WITH P-AMINO BENZAMIDINE

Template:ABSTRACT PUBMED 10467148

About this Structure

1RFN is a Protein complex structure of sequences from Homo sapiens. Full crystallographic information is available from OCA.

Reference

Coagulation factor IXa: the relaxed conformation of Tyr99 blocks substrate binding., Hopfner KP, Lang A, Karcher A, Sichler K, Kopetzki E, Brandstetter H, Huber R, Bode W, Engh RA, Structure. 1999 Aug 15;7(8):989-96. PMID:10467148

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