Cellulose docking domain, dockering superfamily

In anaerobic microorganisms, the degradation of plant cell walls in order to recycle the photosynthetically fixed carbon is carried out by a multifunctional complex termed the cellulosome. The cellulosome consists of a number of independent enzyme components, each of which contains a conserved dockerin domain. The dockerin domain functions to bind the enzyme to a cohesin domain within the protein scaffoldin protein, a multidomain protein containing a cellulose binding module for attachment to the host microorganism. The dockerin-cohesin binding enables the assembly of multiple polysaccharide-degrading enzymes to be brought together into the cellulosome complex. The dockerin sequences of bacterial and fungal enzymes are completely different. Fungal enzymes contain one, two or three copies of the dockerin sequence in tandem within the catalytic polypeptide, while in bacteria such as Clostridium thermocellum, the cellulosome catalytic components contain a single dockerin domain. The tandem dockerin domains, seen in the majority of anaerobic fungal plant cell wall degrading enzymes, could present multiple simultaneous binding sites and, therefore, permit tailoring of binding to catalytic demands. Furthermore, fungal dockerin domains have broad interspecies specificity, while bacterial dockerin domains appear species-specific. The structure of the N-terminal dockerin domain of Cel45A from the anaerobic fungus Piromyces equi displays an alpha/beta fold that is disulphide-rich [11524680].