Crystal Structure of MJ1247 Protein from M. jannaschii at 2.0 Å Resolution Infers a Molecular Function of 3-Hexulose-6-Phosphate Isomerase

The crystal structure of the hypothetical protein MJ1247 from Methanococccus jannaschii at 2 Å resolution, a detailed sequence analysis, and biochemical assays infer its molecular function to be 3-hexulose-6-phosphate isomerase (PHI). In the dissimilatory ribulose monophosphate (RuMP) cycle, ribulose-5-phosphate is coupled to formaldehyde by the 3-hexulose-6-phosphate synthase (HPS), yielding hexulose-6-phosphate, which is then isomerized to fructose-6-phosphate by the enzyme 3-hexulose-6-phosphate isomerase. MJ1247 is an α/β structure consisting of a five-stranded parallel β sheet flanked on both sides by α helices, forming a three-layered α-β-α sandwich. The fold represents the nucleotide binding motif of a flavodoxin type. MJ1247 is a tetramer in the crystal and in solution and each monomer has a folding similar to the isomerase domain of glucosamine-6-phosphate synthase (GlmS).