2j2f

From Proteopedia

Revision as of 12:43, 23 January 2008

THE T199D MUTANT OF STEAROYL ACYL CARRIER PROTEIN DESATURASE FROM RICINUS COMMUNIS (CASTOR BEAN)

Overview

Sequence analysis of the diiron cluster-containing soluble desaturases, suggests they are unrelated to other diiron enzymes; however, structural, alignment of the core four-helix bundle of desaturases to other diiron, enzymes reveals a conserved iron binding motif with similar spacing in all, enzymes of this structural class, implying a common evolutionary ancestry., Detailed structural comparison of the castor desaturase with that of a, peroxidase, rubrerythrin, shows remarkable conservation of both identity, and geometry of residues surrounding the diiron center, with the exception, of residue 199. Position 199 is occupied by a threonine in the castor, desaturase, but the equivalent position in rubrerythrin contains a, glutamic acid. We previously hypothesized that a carboxylate in this, location facilitates oxidase chemistry in rubrerythrin by the close, apposition of a residue capable of facilitating proton transfer to the, activated oxygen (in a hydrophobic cavity adjacent to the diiron center, based on the crystal structure of the oxygen-binding mimic azide). Here we, report that desaturase mutant T199D binds substrate but its desaturase, activity decreases by approximately 2 x 10(3)-fold. However, it shows a, >31-fold increase in peroxide-dependent oxidase activity with respect to, WT desaturase, as monitored by single-turnover stopped-flow spectrometry., A 2.65-A crystal structure of T199D reveals active-site geometry, remarkably similar to that of rubrerythrin, consistent with its enhanced, function as an oxidase enzyme. That a single amino acid substitution can, switch reactivity from desaturation to oxidation provides experimental, support for the hypothesis that the desaturase evolved from an ancestral, oxidase enzyme.

About this Structure

2J2F is a Single protein structure of sequence from Ricinus communis with as ligand. Active as Transferred entry: 1.14.19.2, with EC number 1.14.99.6 Known structural/functional Site: . Full crystallographic information is available from OCA.

Reference

A single mutation in the castor Delta9-18:0-desaturase changes reaction partitioning from desaturation to oxidase chemistry., Guy JE, Abreu IA, Moche M, Lindqvist Y, Whittle E, Shanklin J, Proc Natl Acad Sci U S A. 2006 Nov 14;103(46):17220-4. Epub 2006 Nov 6. PMID:17088542

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