PROSITE documentation PDOC51766

Dockerin domain profile

Plant cell wall polysaccharides comprise the most abundant reservoir of organic carbon in the biosphere. The cellulosomne is a large multienzyme complex used by many anaerobic bacteria for the efficient degradation of plant-cell wall polysaccharides. The principal component of the cellulosome is a scaffoldin subunit, a large enzyme-integrating protein, that contains cohesin modules (usually in multiple copies) for incorporation of the different enzymes and other cellulosomal components. The enzymes contain a complementary type of module, the dockerin domain, that binds tenaciously to the cohesin modules of the scaffoldin subunit [1,2,3,4].

The dockerin domains consist of about 70 amino acid residues and contain two duplicated segments, each of about 22 amino acid residues. The first 12 residues of these duplicated sequences bear remarkable resemblance to the calcium-binding loop of the EF-hand motif (see <PDOC00018>), in which all the calcium-binding residues (i.e., aspartic acids and asparagines) are highly conserved. The second halves of the duplicated sequences appear to form α helices. These helices would be analogous to the F helix of the EF-hand motif [1,2,3,4].

The dockerin domain comprises three α-helices (see <PDB:2MTE>). Helices H1 and H3, which are antiparallel to one another, and the two calcium-binding loops (Ca1 and Ca2) correspond to the tandem duplicated sequences that form the two F-hand motifs. A short loop region and helix H2 connect the F-hand motifs. The 12-residue Ca(2+)-binding loop of each motif coordinates one Ca(2+) ion in the typical pentagonal bipyramid configuration of EF-hand Ca(2+)-binding proteins [3,4].

The profile we developed covers the entire dockerin domain.