Cellulose-binding domains: Classification and properties

More than one hundred and twenty cellulose-binding domains (CBDs) are classified into ten families (I-X). Three families (V, VII and VII) contain only single representatives. Two of the larger families (II and III) can be divided into distinct subfamilies. Most of the CBDs are from cellulases and xylanases but some are from other hydrolases or from non-catalytic proteins. Family I CBDs are all from fungi. With the exception of families VI and XIII, the remaining the families contain only representatives from bacteria. CBDs are found at the N or C termini of proteins or are internal. Representatives of certain families show a tendency to occur at terminal or internal positions and to be associated with representatives of particular catalytic domain families. Possible relationships between the the classification scheme and the functional properties of the CBDs are discussed.