Enzyme processivity changes with the extent of recalcitrant polysaccharide degradation

Glycoside hydrolases depolymerize polysaccharides. They can subtract single carbohydrate chains from polymer crystals and cleave glycosidic bonds without dissociating from the substrate after each catalytic event. This processivity is thought to conserve energy during polysaccharide degradation. Herein, we compare the processivity of components of the chitinolytic machinery of Serratia marcescens. The two processive chitinases ChiA and ChiB, the ChiB-W97A mutant, and the endochitinase ChiC were analyzed for the extent of degradation of three different chitin substrates. Moreover, enzyme processivity was assessed on the basis of the [(GlcNAc)2]/[GlcNAc] product ratio. 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.