X-ray analysis of D-xylose isomerase at 1.9 A: native enzyme in complex with substrate and with a mechanism-designed inactivator

摘要: Abstract The structures of crystalline D-xylose isomerase (D-xylose ketol-isomerase; EC 5.3.1.5) from Streptomyces rubiginosus and its complexes with substrate an active-site-directed inhibitor have been determined by x-ray diffraction techniques refined to 1.9-A resolution. This study identifies the active site, as well two metal-binding sites. The metal ions are important in maintaining structure active-site region one them binds C3-O C5-O forming a six-membered ring. has revealed very close contact between histidine C1 substrate, suggesting that this is base abstracts proton substrate. mechanism-based analog turned over enzyme give product alkylates same histidine, reinforcing our interpretation. changes native enzyme, bound alkylated indicate mechanism involves "open-chain" conformation intermediate isomerization reaction probably cis-ene diol because correctly placed abstract or C2 A water molecule C1O C2O so may act donor acceptor enolization ring-opened