7c8h

Publication Abstract from PubMed

Phosphoketolase and transketolase are thiamine diphosphate-dependent enzymes and play a central role in the primary metabolism of bifidobacteria: the bifid shunt. The enzymes both catalyze phosphorolytic cleavage of xylulose 5-phosphate or fructose 6-phosphate in the first reaction step, but possess different substrate specificity in the second reaction step, where phosphoketolase and transketolase utilize inorganic phosphate (P(i)) and D-ribose 5-phosphate, respectively, as the acceptor substrate. Structures of Bifidobacterium longum phosphoketolase holoenzyme and its complex with a putative inhibitor, phosphoenolpyruvate, were determined at 2.5 A resolution by serial femtosecond crystallography using an X-ray free-electron laser. In the complex structure, phosphoenolpyruvate was present at the entrance to the active-site pocket and plugged the channel to thiamine diphosphate. The phosphate-group position of phosphoenolpyruvate coincided well with those of xylulose 5-phosphate and fructose 6-phosphate in the structures of their complexes with transketolase. The most striking structural change was observed in a loop consisting of Gln546-Asp547-His548-Asn549 (the QN-loop) at the entrance to the active-site pocket. Contrary to the conformation of the QN-loop that partially covers the entrance to the active-site pocket (;closed form') in the known crystal structures, including the phosphoketolase holoenzyme and its complexes with reaction intermediates, the QN-loop in the current ambient structures showed a more compact conformation with a widened entrance to the active-site pocket (;open form'). In the phosphoketolase reaction, the ;open form' QN-loop may play a role in providing the binding site for xylulose 5-phosphate or fructose 6-phosphate in the first step, and the ;closed form' QN-loop may help confer specificity for P(i) in the second step.

Ambient temperature structure of phosphoketolase from Bifidobacterium longum determined by serial femtosecond X-ray crystallography.,Nakata K, Kashiwagi T, Kunishima N, Naitow H, Matsuura Y, Miyano H, Mizukoshi T, Tono K, Yabashi M, Nango E, Iwata S Acta Crystallogr D Struct Biol. 2023 Apr 1;79(Pt 4):290-303. doi: , 10.1107/S2059798323001638. Epub 2023 Mar 28. PMID:36974963^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.