Abstract

Interconversion of D-ribose-5-phosphate (R5P) and D-ribulose-5-phosphate is art important step in the pentose phosphate pathway. Two unrelated enzymes with R5P isomerase activity were first identified in Escherichia coli, RpiA and RpiB. In this organism, the essential 5-carbon sugars were thought to be processed by RpiA, while the primary role of RpiB was suggested to instead be interconversion of the rare 6-carbon sugars D-allose-6-phosphate (Al16P) and D-allulose-6-phosphate. In Mycobacterium tuberculosis, where only an RpiB is found, the 5-carbon sugars are believed to be the enzyme's primary substrates. Here, we present kinetic studies examining the Al16P isomerase activity of the RpiBs from these two organisms and show that only the E. coli enzyme can catalyze the reaction efficiently. Al16P instead acts as an inhibitor of the M. tuberculosis enzyme in its action on R5P. X-ray studies of the M. tuberculosis enzyme co-crystallized with Al16P and 5deoxy-5-phospho-D-ribonohydroxamate (an inhibitor designed to mimic the 6-carbon sugar) and comparison with the E. coli enzyme's structure allowed us to identify differences in the active sites that explain the kinetic results. Two other structures, that of a mutant E. coli RpiB in which histidine 99 was changed to asparagine and that of wild-type M. tuberculosis enzyme, both co-crystallized with the substrate ribose-5-phosphate, shed additional light on the reaction mechanism of RpiBs generally. (C) 2008 Elsevier Ltd. All rights reserved.

Keywords

ribose-5-phosphate isomerase; allose-6-phosphate isomerase; rare sugar; X-ray crystallography; rv2465c

Published in

Journal of Molecular Biology
2008, Volume: 382, number: 3, pages: 667-679
Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD

SLU Authors

• Mowbray, Sherry

  • Department of Molecular Biology, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

Ensure healthy lives and promote well-being for all at all ages


UKÄ Subject classification

Food Science
Biochemistry and Molecular Biology


Publication identifier

DOI: https://doi.org/10.1016/j.jmb.2008.06.090

Permanent link to this page (URI)

https://res.slu.se/id/publ/78143