1mn0
From Proteopedia
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Crystal structure of galactose mutarotase from lactococcus lactis complexed with D-xylose
Overview
Galactose mutarotase catalyzes the conversion of beta-D-galactose to, alpha-D-galactose in the Leloir pathway for galactose metabolism. The high, resolution x-ray structure of the dimeric enzyme from Lactococcus lactis, was recently solved and shown to be topologically similar to the, 18-stranded, anti-parallel beta-motif observed for domain 5 of, beta-galactosidase. In addition to determining the overall molecular fold, of galactose mutarotase, this initial investigation also provided a, detailed description of the electrostatic interactions between the enzyme, and its physiologically relevant substrate, galactose. Specifically, the, side chains of His-96 and His-170 were shown to be located within hydrogen, bonding distance to the C-5 oxygen of the substrate, while the carboxylate, of Glu-304 was positioned near the C-1 hydroxyl group of the sugar. On the, basis of this initial study, a possible role for Glu-304 as the general, acid/base group in catalysis was put forth. Here we describe the combined, x-ray crystallographic and kinetic analyses of L. lactis galactose, mutarotase complexed with D-glucose, D-fucose, D-quinovose, L-arabinose, or D-xylose. These investigations have revealed that there are several, distinct binding modes for these sugars, which are dependent upon the, spatial orientation of the C-4 hydroxyl group. In those sugars with the, same C-4 hydroxyl group orientation as galactose, their C-1 hydroxyl, groups are invariably located near Glu-304. For those sugars, which have, the same C-4 hydroxyl group configuration as glucose, the C-1 hydroxyls, are typically located near Asp-243. These different binding modes, correlate with both the observed kinetic parameters and the presence or, absence of a hydrogen bond between the guanidinium group of Arg-71 and the, C-4 hydroxyl group of the sugar ligand.
About this Structure
1MN0 is a Single protein structure of sequence from Lactococcus lactis with XYS and NI as ligands. Active as Aldose 1-epimerase, with EC number 5.1.3.3 Full crystallographic information is available from OCA.
Reference
Structural and kinetic studies of sugar binding to galactose mutarotase from Lactococcus lactis., Thoden JB, Kim J, Raushel FM, Holden HM, J Biol Chem. 2002 Nov 22;277(47):45458-65. Epub 2002 Sep 5. PMID:12218067
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