The putative compatible solute-binding protein ProX from Mycobacterium tuberculosis H37Rv: biochemical characterization and crystallographic data

In Mycobacterium tuberculosis, the proX gene encodes a putative compatible solute-binding protein (MtProX). However, it was found through sequence alignment that the MtProX protein has very different ligand-binding residues compared with other compatible solute-binding proteins, implying that MtProX may bind to ligands that are as yet uncharacterized. In this work, it was demonstrated that MtProX binds to polyphenols such as phloretin, monoacetylphloroglucinol and 2,4-dihydroxyacetophloroglucinol with dissociation constants between 20 and 70 µM. Crystals of MtProX were obtained using a precipitant consisting of 0.2 M NaCl, 0.1 M Tris pH 8.5, 25%(w/v) polyethylene glycol 3350. The crystals diffracted to 2.10 Å resolution and belonged to space group P4(3)2(1)2, with unit-cell parameters a = b = 90.17, c = 161.92 Å, α = β = γ = 90.0°. Assuming the presence of two MtProX molecules in the asymmetric unit, the Matthews coefficient was calculated to be 2.74 Å(3) Da(−1), which corresponds to a solvent content of 55%.