The Fine Structure of the Cellulosome Defines the Intricacies of Carbohydrate Deconstruction in the Mammalian Gut

Protein-protein interactions play a vital role in many cellular processes. One of the most notable examples is the assembly of the cellulosome, a bacterial multi-enzyme complex that efficiently degrades cellulose and hemicellulose. Cellulosome assembly involves the high-affinity binding of type I enzyme-borne dockerins to repeated cohesin modules located on non-catalytic structural proteins termed scaffoldins. The complex is then anchored to the bacterial surface through the interaction of a C-terminal type II dockerin, present on the primary scaffoldin, to cell-bound cohesins. Initially, the architecture and organization of cellulosomes were thought to rely uniquely on these type I and type II cohesin-dockerin interactions but it was recently suggested that cellulosomes from rumen bacteria have developed divergent type III cohesin-dockerin complexes. In this review we will discuss the recent findings suggesting that a different mechanism operates to organize cellulosomes in the gut of mammals.