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190. Abstract-
A combined structural and functional model of the catalytic
region of cellulose synthase is presented as a prototype for the action
of processive -glycosyltransferases and other glycosyltransferases. A 285
amino acid segment of the Acetobacter xylinum cellulose synthase containing
all the conserved residues in the globular region was subjected to protein
modeling using the genetic algorithm. This region folds into a single large
domain with a topology exhibiting a mixed alpha/beta structure. The predicted
structure serves as a topological outline for the structure of this processive
-glycosyltransferase. By incorporating new site-directed mutagenesis data
and comparative analysis of the conserved aspartic acid residues and the
QXXRW motif we deduce a number of functional implications based on the
structure. This includes location of the UDP¯glucose substrate-binding
cavity, suggestions for the catalytic processing including positions of
conserved and catalytic residues, secondary structure arrangement and domain
organization. Comparisons to cellulose synthases from higher plants (genetic
algorithm based model for cotton CelA1), data from neural network predictions
(PHD), and to the recently experimentally determined structures of the
non-processive SpsA and 4-galactosyltransferase retest and further validate
our structure-function description of this glycosyltransferase.
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