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PDBsum entry 2vs5
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References listed in PDB file
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Key reference
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Title
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Structural basis of udp-Galactose binding by alpha-1,3-Galactosyltransferase (alpha3gt): role of negative charge on aspartic acid 316 in structure and activity.
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Authors
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P.Tumbale,
H.Jamaluddin,
N.Thiyagarajan,
K.Brew,
K.R.Acharya.
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Ref.
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Biochemistry, 2008,
47,
8711-8718.
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PubMed id
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Abstract
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alpha-1,3-Galactosyltransferase (alpha3GT) catalyzes the transfer of galactose
from UDP-galactose to form an alpha 1-3 link with beta-linked galactosides; it
is part of a family of homologous retaining glycosyltransferases that includes
the histo-blood group A and B glycosyltransferases, Forssman glycolipid
synthase, iGb3 synthase, and some uncharacterized prokaryotic
glycosyltransferases. In mammals, the presence or absence of active forms of
these enzymes results in antigenic differences between individuals and species
that modulate the interplay between the immune system and pathogens. The
catalytic mechanism of alpha3GT is controversial, but the structure of an enzyme
complex with the donor substrate could illuminate both this and the basis of
donor substrate specificity. We report here the structure of the complex of a
low-activity mutant alpha3GT with UDP-galactose (UDP-gal) exhibiting a bent
configuration stabilized by interactions of the galactose with multiple residues
in the enzyme including those in a highly conserved region (His315 to Ser318).
Analysis of the properties of mutants containing substitutions for these
residues shows that catalytic activity is strongly affected by His315 and
Asp316. The negative charge of Asp316 is crucial for catalytic activity, and
structural studies of two mutants show that its interaction with Arg202 is
needed for an active site structure that facilitates the binding of UDP-gal in a
catalytically competent conformation.
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