The structure/function relationship of a dual-substrate (βα) 8-isomerase

Abstract

Two structures of phosphoribosyl isomerase A (PriA) from Streptomyces coelicolor, involved in both histidine and tryptophan biosynthesis, were solved at 1.8 Å resolution. A closed conformer was obtained, which represents the first complete structure of PriA, revealing hitherto unnoticed molecular interactions and the occurrence of conformational changes. Inspection of these conformers, including ligand-docking simulations, allowed identification of residues involved in substrate recognition, chemical catalysis and conformational changes. These predictions were validated by mutagenesis and functional analysis. Arg 19 and Ser 81 were shown to play critical roles within the carboxyl and amino phosphate-binding sites, respectively; the catalytic residues Asp 11 and Asp 130 are responsible for both activities; and Thr 166 and Asp 171, which make an unusual contact, are likely to elicit the conformational changes needed for adopting the active site architectures. This represents the first report of the structure/function relationship of this (βα) 8-isomerase.