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J. Cell Biol.,
Volume 140, Number 2, January 26, 1998 431-446
Department of Pathology, Harvard Medical School and Pathology Research, Massachusetts General Hospital, Charlestown
Navy Yard, Boston, Massachusetts 02129
Glycosylation has been implicated in the regulation of CD44-mediated cell binding of hyaluronan
(HA). However, neither the relative contribution of N-
and O-linked glycans nor the oligosaccharide structures
that alter CD44 affinity for HA have been elucidated. To determine the effect of selective alteration of CD44
oligosaccharide composition on the affinity of CD44 for
HA, we developed a novel strategy based on the use of
affinity capillary electrophoresis (ACE). Soluble recombinant CD44-immunoglobulin fusion proteins were overproduced in the mutant CHO cell line ldl-D,
which has reversible defects in both N- and O-linked
oligosaccharide synthesis. Using this cell line, a panel of
recombinant glycosidases, and metabolic glycosidase
inhibitors, CD44 glycoforms with defined oligosaccharide structures were generated and tested for HA affinity by ACE. Because ldl-D cells express endogenous
cell surface CD44, the effect of any given glycosylation
change on the ability of cell surface and soluble CD44
to bind HA could be compared. Four distinct oligosaccharide structures were found to effect CD44-mediated HA binding: (a) the terminal
2,3-linked sialic acid on
N-linked oligosaccharides inhibited binding; (b) the
first N-linked N-acetylglucosamine residue enhanced
binding; (c) O-linked glycans on N-deglycosylated CD44 enhanced binding; and (d) N-acetylgalactosamine incorporation into non-N-linked glycans augmented HA binding by cell surface CD44. The first
three structures induced up to a 30-fold alteration in
the intrinsic CD44 affinity for HA (Kd = 5 to >150
µM). The fourth augmented CD44-mediated cellular
HA avidity without changing the intrinsic HA affinity
of soluble CD44.
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