Catalytic analysis of the validamycin glycosyltransferase (ValG) and enzymatic production of 4''-epi-validamycin A.
ValG is a glycosyltransferase (GT) that is responsible for the glucosylation of validoxylamine A to validamycin A. To explore the potential utilization of ValG as a tool for the production of validamycin analogues, a number of nucleotidyldiphosphate-sugars were evaluated as alternative substrates for ValG. The results indicated that in addition to its natural substrate, UDP-glucose, ValG also efficiently utilized UDP-galactose as sugar donor and resulted in the production of an unnatural compound, 4''-epi-validamycin A. The new compound demonstrated a moderate growth inhibitory activity against the plant fungal pathogen Rhizoctonia solani (= Pellicularia sasakii). A comparative analysis of ValG with its homologous proteins revealed that ValG contains an unusual DTG motif, in place of the DXD motif proposed for metal ion binding and/or NDP-sugar binding and commonly found in other glycosyltransferases. Site-directed mutagenesis of the DTG motif of ValG to DCD altered its preferences for metal ion binding, but did not seem to affect its substrate specificity.
Department of Pharmaceutical Sciences, Oregon State University, Corvallis, Oregon 97331-3507, USA.
Hui
H
Xu
Kazuyuki
K
Minagawa
Linquan
L
Bai
Zixin
Z
Deng
Taifo
T
Mahmud
D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D007294:Inositol / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000737:chemistry; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D012232:Rhizoctonia / Q000187:drug effects* / Q000378:metabolism; D013302:Streptomyces / Q000201:enzymology* / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects
C531433:4''-epi-validamycin A; D000935:Antifungal Agents; C030790:validamycin A; D007294:Inositol; D016695:Glycosyltransferases; C531432:ValG protein, Streptomyces hygroscopicus