Pathways & interactions
Carbohydrate-binding module 3 (IPR001956)
Short name: CBM3
Overlapping homologous superfamilies
- CBM2/CBM3, carbohydrate-binding domain superfamily (IPR008965)
- Carbohydrate-binding module 3 superfamily (IPR036966)
Carbohydrate-binding modules (CBM) have been classified into more than 40 families according to sequence homology. Several cellulolytic enzymes share a conserved region of about 150 amino acid residues, the CBM3 domain [PMID: 1490597]. It has been classified in three different subtypes, termed family IIIa, IIIb and IIIc. The family IIIa (scaffoldin) and IIIb (mainly free enzymes) are closely similar in their primary structures and both types bind strongly to crystalline cellulose [PMID: 8918451, PMID: 11092922]. Members of the family IIIc, fail to bind crystalline cellulose, but serve in a 'helper' capacity by feeding a single incoming cellulose chain into the active site of the neighbouring catalytic module pending hydrolysis [PMID: 9537366, PMID: 9055408].
The CBM3 domain is mainly found C-terminal to the catalytic domain, which correspond to a wide range of bacterial glycosyl hydrolases like family 9, family 5 and family 10.
The crystal structure of CBM3 has been solved [PMID: 8918451]. It consists of nine beta-strands which form a compact domain that has an overall prismatic shape. It is arranged in two antiparallel beta-sheets that stack face-to-face to form a beta sandwich with jelly roll topology. Two defined surfaces, located on opposite sides of the molecule, contain conserved polar and aromatic residues which are probably involved in the binding of the CBM to cellulose [PMID: 8918451, PMID: 11092922]. The first one forms a planar strip whereas the second one forms a shallow groove.
Some proteins known to contain a CBM3 domain are listed below:
- Clostridial cellulosomal scaffolding proteins cipA, cipC and cbpA. They promote the binding of cellulose to the catalytic domains of the cellulolytic enzymes.
- Bacterial cellulases A, B, F, G, I, N, Y, Z (Endo-1,4-beta-glucanase, EC:22.214.171.124).
This entry represents the CBM3 domain, which is also known as cellulose-binding domain family III (CBD III).