Cellulosomes are multi-enzyme complexes. Cellulosomes are associated with the cell surface and mediate cell attachment to insoluble substrates and degrade them to soluble products which are then absorbed. Cellulosome complexes are intricate, multi-enzyme machines, produced by many cellulolytic microorganisms. They are produced by microorganisms for efficient degradation of plant cell wall polysaccharides, notably cellulose, the most abundant organic polymer on Earth. The multiple subunits of cellulosomes are composed of numerous functional domains which interact with each other and with the cellulosic substrate. One of these subunits, a large glycoprotein "scaffoldin", is a distinctive class of non-catalytic scaffolding polypeptides. The scaffoldin subunit selectively integrates the various cellulases and xylanase subunits into the cohesive complex, by combining its cohesin domains with a typical dockerin domain present on each of the subunit enzymes. The scaffoldin of some cellulosomes, an example being that of Clostridium thermocellum, contains a carbohydrate-binding module that adheres cellulose to the cellulosomal complex.