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A motif rich in charged residues determines product specificity in isomaltulose synthase
Author(s) -
Zhang Daohai,
Li Nan,
Swaminathan Kunchithapadam,
Zhang Lian-Hui
Publication year - 2003
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(02)03835-8
Subject(s) - chemistry , glycosyltransferase , biochemistry , sequence motif , enzyme , atp synthase , peptide sequence , structural motif , stereochemistry , dna , gene
Isomaltulose synthase (PalI) catalyzes hydrolysis of sucrose and formation of α‐1,6 and α‐1,1 bonds to produce isomaltulose (α‐ D ‐glucosylpyranosyl‐1,6‐ D ‐fructofranose) and small amount of trehalulose (α‐ D ‐glucosylpyranosyl‐1,1‐ D ‐fructofranose). A potential isomaltulose synthase‐specific motif ( 325 RLDRD 329 ), that contains a ‘DxD’ motif conserved in many glycosyltransferases, was identified based on sequence comparison with reference to the secondary structural features of PalI and homologs. Site‐directed mutagenesis analysis of the motif showed that the four charged amino acid residues (Arg 325 , Arg 328 , Asp 327 and Asp 329 ) influence the enzyme kinetics and determine the product specificity. Mutation of these four residues increased trehalulose formation by 17–61% and decreased isomaltulose by 26–67%. We conclude that the ‘RLDRD’ motif controls the product specificity of PalI.