Cellulosomes - Structure and ultrastructure

The cellulosome is a macromolecular machine, whose components interact in a synergistic manner to catalyze the efficient degradation of cellulose. The cellulosome complex is composed of numerous kinds of cellulases and relate d enzyme subunits, which are assembled into the complex by virtue of a uniq ue type of scaffolding subunit (scaffoldin). Each of the cellulosomal subun its consists of a multiple set of modules, two classes of which (dockerin d omains on the enzymes and cohesin domains on scaffoldin) govern the incorpo ration of the enzymatic subunits into the cellulosome complex. Another scaf foldin module-the cellulose-binding domain-is responsible for binding to th e substrate. Some cellulosomes appear to be tethered to the cell envelope v ia similarly intricate, multiple-domain anchoring proteins. The assemblage is organized into dynamic polycellulosomal organelles, which adorn the cell surface. The cellulosome dictates both the binding of the cell to the subs trate and its extracellular decomposition to soluble sugars, which are then taken up and assimilated by normal cellular processes. (C) 1998 Academic P ress.