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High resolution X-ray structure of galactose mutarotase from Lactococcus lactis
James B Thoden1, Hazel M Holden
1Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA. JBThoden@facstaff.wisc.edu
The Journal of Biological Chemistry
|March 22, 2002
Summary
Galactose mutarotase facilitates galactose metabolism by interconverting its anomers. Structural analysis reveals its beta-sandwich motif and active site, highlighting key residues involved in substrate binding and catalysis.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Galactose mutarotase is crucial for galactose metabolism, catalyzing the interconversion of alpha-D-galactose and beta-D-galactose.
- Understanding the enzyme's structure is key to elucidating its catalytic mechanism.
Purpose of the Study:
- To determine the three-dimensional structure of galactose mutarotase from Lactococcus lactis.
- To identify the active site residues and understand substrate binding.
Main Methods:
- X-ray crystallography was used to determine the enzyme's structure to 1.9-A resolution.
- Analysis of electron density maps to visualize bound galactose and identify interacting residues.
Main Results:
- The dimeric enzyme exhibits a beta-sandwich motif in each subunit.
- The active site is an open cleft containing both alpha- and beta-anomers of galactose.
- Key residues (Arg71, His96, His170, Asp243, Glu304) anchor the substrate.
- Conserved His96 and His170 residues interact with galactose's C-5 oxygen.
- Glu304 is positioned to act as a general acid/base catalyst.
Conclusions:
- The determined structure provides insights into the catalytic mechanism of galactose mutarotase.
- The active site architecture and conserved residues suggest a role for Glu304 in catalysis.