SPECIES-SPECIFICITY OF THE COHESIN-DOCKERIN INTERACTION BETWEEN CLOSTRIDIUM-THERMOCELLUM AND CLOSTRIDIUM-CELLULOLYTICUM - PREDICTION OF SPECIFICITY DETERMINANTS OF THE DOCKERIN DOMAIN

The cross-species specificity of the cohesin-dockerin interaction, whi ch defines the incorporation of the enzymatic subunits into the cellul osome complex, has been investigated, Cohesin-containing segments from the cellulosomes of two different species, Clostridium thermocellum a nd Clostridium cellulolyticum, were allowed to interact with celluloso mal (dockerin-containing) enzymes from each species, In both cases, th e cohesin domain of one bacterium interacted with enzymes from its own cellulosome in a calcium-dependent manner, but the same cohesin faile d to recognize enzymes from the other species, Thus, in the case of th ese two bacteria, the cohesin-dockerin interaction seems to be species -specific, Based on intra-and cross-species sequence comparisons among the different dockerins together with their known specificities, we t ender a prediction as to the aminoacid residues critical to recognitio n of the cohesins. The suspected residues were narrowed down to only f our, which comprise a repeated pair located within the calcium-binding motif of two duplicated sequences, characteristic of the dockerin dom ain, According to the proposed model, these four residues do not parti cipate in the binding of calcium per se; instead, they appear to serve as recognition codes in promoting interaction with the cohesin surfac e. (C) 1997 Wiley-Liss, Inc.