Crystal structures of phosphoketolase: thiamine diphosphate-dependent dehydration mechanism.

Abstract

Thiamine diphosphate (ThDP)-dependent enzymes are ubiquitously present in all organisms and catalyze essential reactions in various metabolic pathways. ThDP-dependent phosphoketolase plays key roles in the central metabolism of heterofermentative bacteria and in the pentose catabolism of various microbes. In particular, bifidobacteria, representatives of beneficial commensal bacteria, have an effective glycolytic pathway called bifid shunt in which 2.5 mol of ATP are produced per glucose. Phosphoketolase catalyzes two steps in the bifid shunt because of its dual-substrate specificity; they are phosphorolytic cleavage of fructose 6-phosphate or xylulose 5-phosphate to produce aldose phosphate, acetyl phosphate, and H(2)O. The phosphoketolase reaction is different from other well studied ThDP-dependent enzymes because it involves a dehydration step. Although phosphoketolase was discovered more than 50 years ago, its three-dimensional structure remains unclear. In this study we report the crystal structures of xylulose 5-phosphate/fructose 6-phosphate phosphoketolase from Bifidobacterium breve. The structures of the two intermediates before and after dehydration (α,β-dihydroxyethyl ThDP and 2-acetyl-ThDP) and complex with inorganic phosphate give an insight into the mechanism of each step of the enzymatic reaction.

• Authors: Ryuichiro Suzuki, Takane Katayama, Byung-Jun Kim, Takayoshi Wakagi, Hirofumi Shoun, Hisashi Ashida, Kenji Yamamoto, Shinya Fushinobu
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 285 Issue 44 Pg. 34279-87 (Oct 29 2010) ISSN: 1083-351X [Electronic] United States
• PMID: 20739284 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Pentosephosphates
• xylulose-5-phosphate
• Adenosine Triphosphate
• Transketolase
• Aldehyde-Lyases
• phosphoketolase
• Glucose
• Thiamine Pyrophosphate

Topics

• Adenosine Triphosphate (chemistry)
• Aldehyde-Lyases (chemistry)
• Bifidobacterium (metabolism)
• Catalysis
• Crystallography, X-Ray (methods)
• Gene Expression Regulation, Bacterial
• Glucose (metabolism)
• Models, Chemical
• Models, Molecular
• Molecular Conformation
• Pentosephosphates (chemistry)
• Substrate Specificity
• Thiamine Pyrophosphate (chemistry)
• Transketolase (chemistry)