Localization of the essential histidine and carboxylate group in D-xylose isomerases.
D-Xylose isomerases from different bacterial strains were chemically modified with histidine and carboxylate-specific reagents. The active-site residues were identified by amino acid sequence analysis of peptides recognized by differential peptide mapping on ligand-protected and unprotected derivatized enzyme. Both types of modified residues were found to cluster in a region with consensus sequence: Phe-His-Asp-Xaa-Asp-Xaa-Xaa-Pro-Xaa-Gly, conserved in all D-xylose isomerases studied so far. These results are consistent with the recently published X-ray data of the enzyme active centre from Streptomyces rubiginosus showing hydrogen bond formation between Asp-57 and His-54 which locks the latter in one tautomeric form. A study of the pH-dependence of the kinetic parameters suggests the participation of a histidine group in the substrate-binding but not in the isomerization process. Comparison of the N-terminal amino acid sequences of several D-xylose isomerases further revealed a striking homology among the Actinomycetaceae enzymes and identifies them as a specific class of D-xylose isomerases.
Vangrysperre
W
W
Laboratory of Biochemistry, State University of Ghent, Belgium.
Van Damme
J
J
Vandekerckhove
J
J
De Bruyne
C K
CK
Cornelis
R
R
Kersters-Hilderson
H
H
D019747:Aldose-Ketose Isomerases; D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006639:Histidine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D013302:Streptomyces / Q000201:enzymology
D006639:Histidine; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase