1k0e
From Proteopedia
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THE CRYSTAL STRUCTURE OF AMINODEOXYCHORISMATE SYNTHASE FROM FORMATE GROWN CRYSTALS
Overview
Aminodeoxychorismate synthase is part of a heterodimeric complex that, catalyzes the two-step biosynthesis of 4-amino-4-deoxychorismate, a, precursor of p-aminobenzoate and folate in microorganisms. In the first, step, a glutamine amidotransferase encoded by the pabA gene generates, ammonia as a substrate that, along with chorismate, is used in the second, step, catalyzed by aminodeoxychorismate synthase, the product of the pabB, gene. Here we report the X-ray crystal structure of Escherichia coli PabB, determined in two different crystal forms, each at 2.0 A resolution. The, 453-residue monomeric PabB has a complex alpha/beta fold which is similar, to that seen in the structures of homologous, oligomeric TrpE subunits of, several anthranilate synthases of microbial origin. A comparison of the, structures of these two classes of chorismate-utilizing enzymes provides a, rationale for the differences in quaternary structures seen for these, enzymes, and indicates that the weak or transient association of PabB with, PabA during catalysis stems at least partly from a limited interface for, protein interactions. Additional analyses of the structures enabled the, tentative identification of the active site of PabB, which contains a, number of residues implicated from previous biochemical and genetic, studies to be essential for activity. Differences in the structures, determined from phosphate- and formate-grown crystals, and the location of, an adventitious formate ion, suggest that conformational changes in loop, regions adjacent to the active site may be needed for catalysis. A, surprising finding in the structure of PabB was the presence of a, tryptophan molecule deeply embedded in a binding pocket that is analogous, to the regulatory site in the TrpE subunits of the anthranilate synthases., The strongly bound ligand, which cannot be dissociated without, denaturation of PabB, may play a structural role in the enzyme since there, is no effect of tryptophan on the enzymic synthesis of, aminodeoxychorismate. Extensive sequence similarity in the, tryptophan-binding pocket among several other chorismate-utilizing, enzymes, including isochorismate synthase, suggests that they too may bind, tryptophan for structural integrity, and corroborates early ideas on the, evolution of this interesting enzyme family.
About this Structure
1K0E is a Single protein structure of sequence from Escherichia coli with TRP and FMT as ligands. Full crystallographic information is available from OCA.
Reference
Structure of Escherichia coli aminodeoxychorismate synthase: architectural conservation and diversity in chorismate-utilizing enzymes., Parsons JF, Jensen PY, Pachikara AS, Howard AJ, Eisenstein E, Ladner JE, Biochemistry. 2002 Feb 19;41(7):2198-208. PMID:11841211
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