Effect of rational mutagenesis of selected cohesin residues on the high-affinity cohesin-dockerin interaction

The high-affinity cohesin-dockerin interaction that dictates cellulosome assembly was probed by site-directed mutagenesis of suspected recognition residues on the cohesin domain. The involvement of two loops that flank the 8,3,6,5 β sheet of a cohesin domain of the cellulosomal scaffoldin from Clostridium thermocellum was examined by their partial replacement with analogous portions of a cohesin domain from Clostridium cellulolyticum. Similarly, several amino acids located on this (3 sheet were replaced with matching residues on the counter species cohesin. The dockerin-binding specificity of the cohesin was not altered by those mutations. However, the binding affinity of certain mutants significantly decreased, thus corroborating the notion that the dockerin-binding site stretches along this particular face of the cohesin molecule and that some of the mutated surface residues play a significant role in the binding process.