title: Alternative epimerization in C(7)N-aminocyclitol biosynthesis is catalyzed by ValD, a large protein of the vicinal oxygen chelate superfamily.
abstract: Gene valD, encodes a large vicinal oxygen chelate (VOC) superfamily protein, has been identified in the validamycin biosynthetic gene cluster. Inactivation of valD significantly reduced validamycin A production, which was fully restored with the full-length valD and partially restored with either N-terminal or C-terminal half by complementation. Heterologously expressed ValD catalyzed the epimerization of 2-epi-5-epi-valiolone to 5-epi-valiolone. This metalloenzyme is a homodimer with a metal ion-binding ratio of 0.73 mol/mole protein toward Fe(2+), Mn(2+), Ni(2+), and Zn(2+). Individual and combined site-directed mutations of eight putative active site residues revealed that the N-terminal H44/E107 and the C-terminal H315/E366 are more critical for the activity than the internal H130, E183, H229, and E291. Our data have established ValD as one of the largest proteins of the VOC superfamily, catalyzing an alternative epimerization for C(7)N-aminocyclitol biosynthesis.
authors.affiliation: Shanghai Jiao Tong University, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Xu
authors.forename: Yirong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jongtae
authors.initials: J
authors.lastname: Yang
authors.forename: Taifo
authors.initials: T
authors.lastname: Mahmud
authors.forename: Linquan
authors.initials: L
authors.lastname: Bai
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D007294:Inositol / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry; D008667:Metalloproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology
chemical_list: C433384:5-epi-(6-(2)H2)valiolone; D001426:Bacterial Proteins; D008667:Metalloproteins; D050505:Mutant Proteins; D007294:Inositol; C003749:validamycins