Fig. 6

Intricacy of the B. cellulosolvens cellulosome assemblies. The scheme shows possible interactions among scaffoldins and enzymatic modules, as derived from examination of interactions by affinity ELISA, where binding specificities of the cohesin-borne scaffoldins are detailed in Fig. 4. The type II enzyme-borne dockerins generally bound very strongly to the cohesins of ScaA1/A2, ScaJ, ScaH1/H2, ScaL1/L2 and ScaM1/M2, ScaO and ScaV. The type I dockerins of ScaA1 and its ScaA2 sibling interacted strongly with the multiplicity of ScaB cohesins and the singular cohesin of ScaF2, which would anchor them and their associated enzymes to the B. cellulosolvens cell surface. Single enzymes can also be anchored directly to the cell wall via type II interaction with the ScaJ cohesin. Large secreted cell-free assemblies would ensue from strong type I interactions between the ScaA1/A2 dockerins with the cohesins of ScaE and ScaS. Smaller cell-free complexes would comprise the direct type II interaction between enzymes and ScaM1 and ScaM2, both of which contain a CBM3 for targeting to the cellulosic substrate. Finally, the strong type I interaction between the ScaR3 dockerin and the single F1 cohesin would serve to connect the group-R scaffoldins to the cell surface. All other cohesin–dockerin interactions detected within the framework of this study appeared to be much weaker, and the resultant complexes would presumably be less stable. ScaW1, ScaW2, and ScaG were not tested empirically, owing to their late discovery