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The thermodynamics of binding of concanavalin A (Con A) with a series of linear
and branched chain oligosaccharides including certain N-linked complex type and
oligomannose type carbohydrates and a fraction of quail ovalbumin containing
Man7 and Man8 oligomannose chains have been determined using titration
microcalorimetry.
Methyl3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, a branch chain
trisaccharide moiety found in all N-linked carbohydrates which possesses
approximately 60-fold higher affinity than methyl alpha-D-mannopyranoside,
exhibited a change in enthalpy of binding (delta H) of -14.4 kcal mol-1 as
compared to -8.2 kcal mol-1 for the monosaccharide. This demonstrates that Con A
possesses an extended binding site for the trimannoside. However, a biantennary
complex type carbohydrate with terminal beta (1,2)-GlcNAc residues which binds
with 3-fold higher affinity than the trimannoside possesses a delta H of only
-10.6 kcal mol-1. A plot of -delta H versus -T delta S for the carbohydrates in
the present study showed positive deviations in -T delta S for the complex type
carbohydrate, as well as alpha (1,2)-di- and trimannosyl oligosaccharides which
are part of the structures of oligomannose type carbohydrates. The relative
favorable changes in binding entropies of these compounds are attributed to the
presence of multiple internal and terminal residues in each molecule which can
independently bind to the monosaccharide binding site of the lectin. The delta H
values for the complex type carbohydrate and the alpha (1,2) mannose
oligosaccharides were also approximately -2.5 kcal mol-1 greater than that of
methyl alpha-D-mannopyranoside, indicating some extended binding site
interactions.(ABSTRACT TRUNCATED AT 250 WORDS)
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