Multistate binding in pyridoxine 5'-phosphate synthase: 1.96 A crystal structure in complex with 1-deoxy-D-xylulose...

We report the 1.96 A crystal structure of pyridoxine 5'-phosphate synthase (PdxJ) in complex with 1-deoxy-D-xylulose phosphate (dXP). The octameric enzyme possesses eight distinct binding sites, and three different binding states are observed. The observation of these three states supports a mechanism in which precise conformational changes of a peptide loop and groups of active site residues modulate binding and specificity. The differences in protein conformation when one or two substrates are bound can be correlated with a condensation mechanism that leads productively to the formation of pyridoxine 5'-phosphate (PNP). "Snapshots" of the progression from the apo form to a singly occupied "transitional binding" state and, subsequently, to a fully occupied, reactive state are revealed and indicate how the enzyme structure can be related to a plausible catalytic mechanism and, moreover, to favorable energetics of reaction.