Conserved Cys residue influences catalytic properties of potato endo-(1-->3)-beta-glucanase GLUB20-2.

The synthesis and degradation of (1-->3)-beta-glycosidic bonds between glucose moieties are essential metabolic processes in plant cell architecture and function. We have found that a unique, conserved cysteine residue, positioned outside the catalytic centre of potato endo-(1-->3)-beta-glucanase - product of the gluB20-2 gene, participates in determining the substrate specificity of the enzyme. The same residue is largely responsible for endo-(1-->3)-beta-glucanase inhibition by mercury ions. Our results confirm that the spatial adjustment between an enzyme and its substrate is one of the essential factors contributing to the specificity and accuracy of enzymatic reactions.