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'''Crystal Structure of Apo-Habu IX-bp at pH 4.6''' | '''Crystal Structure of Apo-Habu IX-bp at pH 4.6''' | ||
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[[Category: Morita, T.]] | [[Category: Morita, T.]] | ||
[[Category: Suzuki, N.]] | [[Category: Suzuki, N.]] | ||
[[Category: | [[Category: C-type lectin-like protein]] | ||
[[Category: | [[Category: Domain swapping]] | ||
[[Category: | [[Category: Heterodimer]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 14:27:43 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 11:27, 3 May 2008
Crystal Structure of Apo-Habu IX-bp at pH 4.6
Overview
Coagulation factor IX-binding protein, isolated from Trimeresurus flavoviridis (IX-bp), is a C-type lectin-like protein. It is an anticoagulant consisting of homologous subunits, A and B. Each subunit has a Ca(2+)-binding site with a unique affinity (K(d) values of 14muM and 130muM at pH 7.5). These binding characteristics are pH-dependent and, under acidic conditions, the Ca(2+) binding of the low-affinity site was reduced considerably. In order to identify which site has high affinity and to investigate the pH-dependent Ca(2+) release mechanism, we have determined the crystal structures of IX-bp at pH 6.5 and pH 4.6 (apo form), and compared the Ca(2+)-binding sites with each other and with those of the solved structures under alkaline conditions; pH 7.8 and pH 8.0 (complexed form). At pH 6.5, Glu43 in the Ca(2+)-binding site of subunit A displayed two conformations. One (minor) is that in the alkaline state, and the other (major) is that at pH 4.6. However, the corresponding Gln43 residue of subunit B is in only a single conformation, which is almost identical with that in the alkaline state. At pH 4.6, Glu43 of subunit A adopts a conformation similar to that of the major conformer observed at pH 6.5, while Gln43 of subunit B assumes a new conformation, and both Ca(2+) positions are occupied by water molecules. These results showed that Glu43 of subunit A is much more sensitive to protonation than Gln43 of subunit B, and the conformational change of Glu43 occurs around pH6.5, which may correspond to the step of Ca(2+) release.
About this Structure
1X2W is a Protein complex structure of sequences from Trimeresurus flavoviridis. Full crystallographic information is available from OCA.
Reference
pH-Dependent structural changes at Ca(2+)-binding sites of coagulation factor IX-binding protein., Suzuki N, Fujimoto Z, Morita T, Fukamizu A, Mizuno H, J Mol Biol. 2005 Oct 14;353(1):80-7. PMID:16165155 Page seeded by OCA on Sat May 3 14:27:43 2008
