1yro
From Proteopedia
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'''Crystal structure of beta14,-galactosyltransferase mutant ARG228Lys in complex with alpha-lactalbumin in the presence of UDP-galactose and Mn''' | '''Crystal structure of beta14,-galactosyltransferase mutant ARG228Lys in complex with alpha-lactalbumin in the presence of UDP-galactose and Mn''' | ||
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[[Category: Qasba, P K.]] | [[Category: Qasba, P K.]] | ||
[[Category: Ramakrishnan, B.]] | [[Category: Ramakrishnan, B.]] | ||
| - | [[Category: | + | [[Category: Arg228lys mutation]] |
| - | [[Category: | + | [[Category: Udp-gal complex]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 16:41:53 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 13:41, 3 May 2008
Crystal structure of beta14,-galactosyltransferase mutant ARG228Lys in complex with alpha-lactalbumin in the presence of UDP-galactose and Mn
Overview
Beta-1,4-galactosyltransferase I (beta4Gal-T1) normally transfers Gal from UDP-Gal to GlcNAc in the presence of Mn(2+) ion (Gal-T activity) and also transfers Glc from UDP-Glc to GlcNAc (Glc-T activity), albeit at only 0.3% efficiency. In addition, alpha-lactalbumin (LA) enhances this Glc-T activity more than 25 times. Comparison of the crystal structures of UDP-Gal- and UDP-Glc-bound beta4Gal-T1 reveals that the O4 hydroxyl group in both Gal and Glc moieties forms a hydrogen bond with the side chain carboxylate group of Glu317. The orientation of the O4 hydroxyl of glucose causes a steric hindrance to the side chain carboxylate group of Glu317, accounting for the enzyme's low Glc-T activity. In this study, we show that mutation of Arg228, a residue in the vicinity of Glu317, to lysine (R228K-Gal-T1) results in a 15-fold higher Glc-T activity, which is further enhanced by LA to nearly 25% of the Gal-T activity of the wild type. The kinetic parameters indicate that the main effect of the mutation of Arg228 to lysine is on the k(cat) of Glc-T, which increases 3-4-fold, both in the absence and in the presence of LA; simultaneously, the k(cat) for the Gal-T reaction is reduced 30-fold. The crystal structure of R228K-Gal-T1 complexed with LA, UDP-Gal, and Mn(2+) determined at 1.9 A resolution shows that the Asp318 side chain exhibits a minor alternate conformation, compared to that in the wild type. This alternate conformation now causes a steric hindrance to the O4 hydroxyl group of the Gal moiety of UDP-Gal, probably causing the dissociation of UDP-Gal and the reduced k(cat) of the Gal-T reaction.
About this Structure
1YRO is a Protein complex structure of sequences from Bos taurus and Mus musculus. Full crystallographic information is available from OCA.
Reference
Mutation of arginine 228 to lysine enhances the glucosyltransferase activity of bovine beta-1,4-galactosyltransferase I., Ramakrishnan B, Boeggeman E, Qasba PK, Biochemistry. 2005 Mar 8;44(9):3202-10. PMID:15736931 Page seeded by OCA on Sat May 3 16:41:53 2008
