1nss
Crystal structure of galactose mutarotase from Lactococcus lactis mutant D243A complexed with glucose
|
OverviewOverview
Galactose mutarotase catalyzes the first step in normal galactose, metabolism by catalyzing the conversion of beta-D-galactose to, alpha-D-galactose. The structure of the enzyme from Lactococcus lactis was, recently solved in this laboratory and shown to be topologically similar, to domain 5 of beta-galactosidase. From this initial X-ray analysis, four, amino acid residues were demonstrated to be intimately involved in sugar, binding to the protein: His 96, His 170, Asp 243, and Glu 304. Here we, present a combined X-ray crystallographic and kinetic analysis designed to, examine the role of these residues in the reaction mechanism of the, enzyme. For this investigation, the following site-directed mutant, proteins were prepared: H96N, H170N, D243N, D243A, E304Q, and E304A. All, of the structures of these proteins, complexed with either glucose or, galactose, were solved to a nominal resolution of 1.95 A or better, and, their kinetic parameters were measured against D-galactose, D-glucose, L-arabinose, or D-xylose. From these studies, it can be concluded that Glu, 304 and His 170 are critical for catalysis and that His 96 and Asp 243 are, important for proper substrate positioning within the active site., Specifically, Glu 304 serves as the active site base to initiate the, reaction by removing the proton from the C-1 hydroxyl group of the sugar, substrate and His 170 functions as the active site acid to protonate the, C-5 ring oxygen.
About this StructureAbout this Structure
1NSS is a Single protein structure of sequence from Lactococcus lactis with GLC and NA as ligands. Active as Aldose 1-epimerase, with EC number 5.1.3.3 Full crystallographic information is available from OCA.
ReferenceReference
The catalytic mechanism of galactose mutarotase., Thoden JB, Kim J, Raushel FM, Holden HM, Protein Sci. 2003 May;12(5):1051-9. PMID:12717027
Page seeded by OCA on Sat Nov 24 23:43:19 2007