Preliminary crystallographic analysis of two hypothetical ribose-5-phosphate isomerases from Streptococcus mutans

Study of the enzymes from sugar metabolic pathways may provide a better understanding of the pathogenesis of the human oral pathogen Streptococcus mutans. Bioinformatics, biochemical and crystallization methods were used to characterize and understand the function of two putative ribose-5-phosphate isomerases: SMU1234 and SMU2142. The proteins were cloned and constructed with N-terminal His tags. Protein purification was performed by Ni²⁺-chelating and size-exclusion chromatography. The crystals of SUM1234 diffracted to 1.9 Å resolution and belonged to space group P2₁2₁2₁, with unit-cell parameters a = 48.97, b = 98.27, c = 101.09 Å, α = β = γ = 90°. The optimized SMU2142 crystals diffracted to 2.7 Å resolution and belonged to space group P1, with unit-cell parameters a = 53.7, b = 54.1, c = 86.5 Å, α = 74.2, β = 73.5, γ = 83.7°. Initial phasing of both proteins was attempted by molecular replacement; the structure of SMU1234 could easily be solved, but no useful results were obtained for SMU2142. Therefore, SeMet-labelled SMU2142 will be prepared for phasing.