J. Biol. Chem., Vol. 262, Issue 4, 1449-1455, Feb, 1987
The three-dimensional structure of acarbose bound to glycogen phosphorylase
EJ Goldsmith, RJ Fletterick and SG Withers
Acarbose, a pseudotetrasaccharide with a conduritol ring at the nonreducing
terminus, is a naturally occurring inhibitor of amylases. It is shown here
to be an inhibitor of glycogen phosphorylase and to bind more tightly to
the enzyme than the equivalent malto- oligosaccharide substrate. X-ray
crystallographic studies of the acarbose-phosphorylase a complex in the
presence of glucose and caffeine reveal the structure of acarbose as bound
to the storage site of phosphorylase. The acarbose binds in an orientation
such that the conduritol ring makes no protein contacts. As with malto-
oligosaccharides bound at this site, the observed conformation of acarbose
is stabilized by O-2-O-3' hydrogen bonding and is similar to, but not
identical with, that predicted by hard-sphere exo-anomeric effect
calculations and justified by 1H nuclear magnetic resonance studies (Bock,
K., and Pedersen, H. (1984) Carbohydr. Res. 132, 142- 149). Intramolecular
O2-O3' hydrogen bonds appear to play an important role in stabilizing the
conformation observed in these studies, even for those residues closely
associated with the protein.