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Description
In bacteria, tryptophan synthesis is performed by the enzymes encoded in the trp operon. The product of the
trpC gene, indole-3-glycerol phosphate synthase (IGPS) catalyzes the indole-forming reaction of tryptophan
synthesis. The reaction mechanism includes a decarboxylation step of the substrate 1-(o-carboxyphenylamino)
1-deoxyribulose 5-phosphate (CdRP). The decarboxylation has been assumed to constitute an essential step
of the mechanism since no activity with the decarboxylated variant of the substrate, phenylaminodeoxyribulosephosphate
(PAdRP), was observed in an early study on IGPS from Escherichia coli (Smith and Yanofsky,
1962).
In this study, we demonstrate enzyme-catalyzed formation of the native product IGP from decarboxylated
substrate PAdRP using IGPS from Pseudomonas aeruginosa. Moreover, the crystal structure of P. aeruginosa
IGPS in complex with a substrate analogue was solved to 2.1 Å resolution. By structural comparison to E.coli
IGPS (Wilmanns et al., 1992), we provide structure-based hypotheses on the difference in substrate specificity
between the E.coli and P. aeruginosa homologs.
References:
Smith, B. O. H. and Yanofsky, C. (1962) ‘Enzymes Involved in the Biosynthesis of Tryptophan’, Methods Enzymol.,
5, pp. 794–806.
Wilmanns, M. et al. (1992) ‘Three-dimensional structure of the bifunctional enzyme phosphoribosylanthranilate
isomerase: Indoleglycerolphosphate synthase from Escherichia coli refined at 2.0 Å resolution’, Journal
of Molecular Biology, 223(2), pp. 477–507.
