Reference "Three-dimensional structures of two plant beta-glucan endohydrolases with distinct substrate specificities"

Reference ID

8625

Title

Three-dimensional structures of two plant beta-glucan endohydrolases with distinct substrate specificities

Source

Proceedings of the National Academy of Sciences of the United States of America, 1994, vol. 91, pp. 2785-2789

Authors (6)

Varghese-J-N	Garrett-T-P
Colman-P-M	Chen-L
Hoj-P-B	Fincher-G-B

Abstract

The three-dimensional structures of (1-->3)-beta-glucanase (EC 3.2.1.39)
isoenzyme GII and (1-->3,1-->4)-beta-glucanase (EC 3.2.1.73) isoenzyme EII from
barley have been determined by x-ray crystallography at 2.2- to 2.3-A
resolution. The two classes of polysaccharide endohydrolase differ in their
substrate specificity and function. Thus, the (1-->3)-beta-glucanases, which are
classified amongst the plant "pathogenesis-related proteins," can hydrolyze (1-->3)-
and (1-->3,1-->6)-beta-glucans of fungal cell walls and may therefore contribute
to plant defense strategies, while the (1-->3,1-->4)-beta-glucanases function in
plant cell wall hydrolysis during mobilization of the endosperm in germinating
grain or during the growth of vegetative tissues. Both enzymes are alpha/beta-
barrel structures. The catalytic amino acid residues are located within deep
grooves which extend across the enzymes and which probably bind the substrates.
Because the polypeptide backbones of the two enzymes are structurally very
similar, the differences in their substrate specificities, and hence their
widely divergent functions, have been acquired primarily by amino acid
substitutions within the groove.