Enzyme processivity changes with the extent of recalcitrant polysaccharide degradation

Abstract

: Polysaccharide depolymerization in nature is primarily accomplished by processive glycoside hydrolases which abstract single carbohydrate chains from polymer crystals and cleave glycosidic bonds without dissociating from the substrate after each catalytic event. Processivity is thought to conserve energy during enzymatic polysaccharide degradation. Herein, we compare two processive chitinases, ChiA and ChiB, one mutant, ChiB-W97A, and the endochitinase ChiC of the wellcharacterized chitinolytic machinery of Serratia marcescens by monitoring the extent of degradation on three different chitin substrates, and using the [(GlcNAc)2]/[GlcNAc] product ratio as a measure of processivity. The results show that the apparent processivity (Papp) greatly diminishes with the extent of degradation and confirm the hypothesis that Papp is limited by the length of obstacle free path on the substrate.