Structural insights into the monosaccharide specificity of Escherichia coli rhamnose mutarotase.
The crystal structure of Escherichia coli rhamnose mutarotase (YiiL) is completely different from the previously reported structures of the Lactococcus lactis galactose mutarotase and the Bacillus subtilis RbsD (pyranase). YiiL exists as a locally asymmetric dimer, which is stabilized by an intermolecular beta-sheet, various hydrophobic interactions, and a cation-pi interaction with a salt-bridge. The protein folds of YiiL are similar to those of a Streptomyces coelicolor mono-oxygenase and a hypothetical Arabidopsis thaliana protein At3g17210. By assaying the enzymatic activity of six active-site mutants and by comparing the crystal structure-derived active site conformations of YiiL, RbsD, and a galactose mutarotase, we were able to define the amino acid residues required for catalysis and suggest a possible catalytic mechanism for YiiL. Although the active-site amino acid residues of YiiL (His, Tyr, and Trp) differ greatly from those of galactose mutarotase (His, Glu, and Asp), their geometries, which determine the structures of the preferred monosaccharide substrates, are conserved. In addition, the in vivo function of YiiL was assessed by constructing a mutant E.coli strain that carries a yiiL deletion. The presence of the yiiL gene is critical for efficient cell growth only when concentrations of l-rhamnose are limited.
Ryu
Kyoung-Seok
KS
Yusong-Gu, Yeoeun-Dong 52, Magnetic Resonance Team, Korea Basic Science Institute, Daejon 305-333, South Korea.
Kim
Jung-In
JI
Cho
Sung-Jae
SJ
Park
Dongkyu
D
Park
Chankyu
C
Cheong
Hae-Kap
HK
Lee
Jie-Oh
JO
Choi
Byong-Seok
BS
D000595:Amino Acid Sequence; D002238:Carbohydrate Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012210:Rhamnose / Q000378:metabolism*; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013379:Substrate Specificity / Q000235:genetics / Q000502:physiology; D013997:Time Factors
D029968:Escherichia coli Proteins; D002238:Carbohydrate Epimerases; C501328:rhamnose mutarotase, E coli; D012210:Rhamnose