title: Mycobacterium tuberculosis ribose-5-phosphate isomerase has a known fold, but a novel active site.
abstract: Ribose-5-phosphate isomerases (EC 5.3.1.6) inter-convert ribose-5-phosphate and ribulose-5-phosphate. This reaction allows the synthesis of ribose from other sugars, as well a means for salvage of carbohydrates after nucleotide breakdown. Two unrelated types of enzyme are known to catalyze the isomerization. The most common one, RpiA, is present in almost all organisms. The second type, RpiB, is found in many bacterial species.Here, we demonstrate that the RpiB from Mycobacterium tuberculosis (Rv2465c) has catalytic properties very similar to those previously reported for the Escherichia coli RpiB enzyme. Further, we report the structure of the mycobacterial enzyme, solved by molecular replacement and refined to 1.88A resolution. Comparison with the E.coli structure shows that there are important differences in the two active sites, including a change in the position and nature of the catalytic base. Sequence comparisons reveal that the M.tuberculosis and E.coli RpiB enzymes are in fact representative of two distinct sub-families. The mycobacterial enzyme represents a type found only in actinobacteria, while the enzyme from E.coli is typical of that seen in many other bacterial proteomes. Both RpiBs are very different from RpiA in structure as well as in the construction of the active site. Docking studies allow additional insights into the reactions of all three enzymes, and show that many features of the mechanism are preserved despite the different catalytic components.
authors.affiliation: Department of Cell and Molecular Biology, Uppsala University, Biomedical Center, Box 596, SE-751 24 Uppsala, Sweden.
authors.forename: Annette K
authors.initials: AK
authors.lastname: Roos
authors.forename: C Evalena
authors.initials: CE
authors.lastname: Andersson
authors.forename: Terese
authors.initials: T
authors.lastname: Bergfors
authors.forename: Micael
authors.initials: M
authors.lastname: Jacobsson
authors.forename: Anders
authors.initials: A
authors.lastname: Karlén
authors.forename: Torsten
authors.initials: T
authors.lastname: Unge
authors.forename: T Alwyn
authors.initials: TA
authors.lastname: Jones
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Mowbray
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D019747:Aldose-Ketose Isomerases; C022548:ribosephosphate isomerase