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.
Xu
Hui
H
Department of Pharmaceutical Sciences, Oregon State University, Corvallis, Oregon 97331-3507, USA.
Minagawa
Kazuyuki
K
Bai
Linquan
L
Deng
Zixin
Z
Mahmud
Taifo
T
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