1igx
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(New page: 200px<br /><applet load="1igx" size="450" color="white" frame="true" align="right" spinBox="true" caption="1igx, resolution 3.1Å" /> '''Crystal Structure of ...)
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Revision as of 15:16, 20 November 2007
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Crystal Structure of Eicosapentanoic Acid Bound in the Cyclooxygenase Channel of Prostaglandin Endoperoxide H Synthase-1.
Overview
Prostaglandin endoperoxide H synthases-1 and -2 (PGHSs) can oxygenate, 18-22 carbon polyunsaturated fatty acids, albeit with varying, efficiencies. Here we report the crystal structures of eicosapentaenoic, acid (EPA, 20:5 n-3) and linoleic acid (LA, 18:2 n-6) bound in the, cyclooxygenase active site of Co(3+) protoporphyrin IX-reconstituted ovine, PGHS-1 (Co(3+)-oPGHS-1) and compare the effects of active site, substitutions on the rates of oxygenation of EPA, LA, and arachidonic acid, (AA). Both EPA and LA bind in the active site with orientations similar to, those seen previously with AA and dihomo-gamma-linolenic acid (DHLA). For, EPA, the presence of an additional double bond (C-17/C-18) causes this, substrate to bind in a "strained" conformation in which C-13 is misaligned, with respect to Tyr-385, the residue that abstracts hydrogen from, substrate fatty acids. Presumably, this misalignment is responsible for, the low rate of EPA oxygenation. For LA, the carboxyl half binds in a more, extended configuration than AA, which results in positioning C-11 next to, Tyr-385. Val-349 and Ser-530, recently identified as important, determinants for efficient oxygenation of DHLA by PGHS-1, play similar, roles in the oxygenation of EPA and LA. Approximately 750- and 175-fold, reductions in the oxygenation efficiency of EPA and LA were observed with, V349A oPGHS-1, compared with a 2-fold change for AA. Val-349 contacts C-2, and C-3 of EPA and C-4 of LA orienting the carboxyl halves of these, substrates so that the omega-ends are aligned properly for hydrogen, abstraction. An S530T substitution decreases the V(max)/K(m) of EPA and LA, by 375- and 140-fold. Ser-530 makes six contacts with EPA and four with LA, involving C-8 through C-16; these interactions influence the alignment of, the substrate for hydrogen abstraction. Interestingly, replacement of, Phe-205 increases the volume of the cyclooxygenase site allowing EPA to be, oxygenated more efficiently than with native oPGHS-1.
About this Structure
1IGX is a Single protein structure of sequence from Ovis aries with BOG, GLC, COH and EPA as ligands. Active as D-amino-acid dehydrogenase, with EC number 1.4.99.1 Full crystallographic information is available from OCA.
Reference
Structure of eicosapentaenoic and linoleic acids in the cyclooxygenase site of prostaglandin endoperoxide H synthase-1., Malkowski MG, Thuresson ED, Lakkides KM, Rieke CJ, Micielli R, Smith WL, Garavito RM, J Biol Chem. 2001 Oct 5;276(40):37547-55. Epub 2001 Jul 27. PMID:11477109
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