1t6k

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spinqualitylabelsall models 1t6k, resolution 1.80Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal structure of phzF from Pseudomonas fluorescens 2-79

Overview

Phenazines, including pyocyanin and iodonin, are biologically active, compounds that are believed to confer producing organisms with a, competitive growth advantage, and also are thought to be virulence factors, in certain diseases including cystic fibrosis. The basic, tricyclic, phenazine ring system is synthesized in a series of poorly characterized, steps by enzymes encoded in a seven-gene cistron in Pseudomonas and other, organisms. Despite the biological importance of these compounds, and our, understanding of their mode of action, the biochemistry and mechanisms of, phenazine biosynthesis are not well resolved. Here we report the 1.8 A, crystal structure of PhzF, a key enzyme in phenazine biosynthesis, solved, by molecular replacement. PhzF is structurally similar to the lysine, biosynthetic enzyme diaminopimelate epimerase, sharing an unusual fold, consisting of two nearly identical domains with the active site located in, an occluded cleft between the domains. Unlike diaminopimelate epimerase, PhzF is a dimer in solution. The two apparently independent active sites, open toward opposite sides of the dimer and are occupied by sulfate ions, in the structure. In vitro experiments using a mixture of purified PhzF, -A, -B, and -G confirm that phenazine-1-carboxylic acid (PCA) is readily, produced from trans-2,3-dihydro-3-hydroxyanthranilic acid (DHHA) without, aid of other cellular factors. PhzA, -B, and -G have no activity toward, DHHA. However, in the presence of PhzF, individually or in combinations, they accelerate the formation of PCA from DHHA and therefore appear to, function after the action of PhzF. Surprisingly, PhzF is itself capable of, producing PCA, albeit slowly, from DHHA. These observations suggest that, PhzF catalyzes the initial step in the conversion of DHHA to PCA, probably, via a rearrangement reaction yielding the more reactive 3-oxo analogue of, DHHA, and that subsequent steps can occur spontaneously. A hypothetical, model for how DHHA binds to the PhzF active site suggests that Glu45 and, Asp208 could act as general acid-base catalysts in a rearrangement, reaction. Given that four reactions lie between DHHA and PCA, ketone, formation, ring formation, decarboxylation, and oxidation, we hypothesize, that the similar PhzA and -B proteins catalyze ring formation and thus may, be more than noncatalytic accessory proteins. PhzG is almost certainly an, oxidase and is predicted to catalyze the final oxidation/aromatization, reaction.

About this Structure

1T6K is a Single protein structure of sequence from Pseudomonas fluorescens with SO4 as ligand. Full crystallographic information is available from OCA.

Reference

Structure and function of the phenazine biosynthesis protein PhzF from Pseudomonas fluorescens 2-79., Parsons JF, Song F, Parsons L, Calabrese K, Eisenstein E, Ladner JE, Biochemistry. 2004 Oct 5;43(39):12427-35. PMID:15449932

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