Carbohydrate Binding Module 6 (CBM6); appended to glycoside hydrolase (GH) domains, including GH5 (cellulase)
This family includes carbohydrate binding module 6 (CBM6) domains that are appended to several glycoside hydrolase (GH) domains, including GH5 (cellulase) and GH16, as well as to coagulation factor 5/8 carbohydrate-binding domains. CBM6s are non-catalytic carbohydrate binding domains that facilitate the strong binding of the GH catalytic modules with their dedicated, insoluble substrates. The CBM6s are appended to GHs that display a diversity of substrate specificities. For some members of this family information is available about the specific substrates of the appended GH domains. It includes the CBM domains of various enzymes involved in cell wall degradation including, an extracellular beta-1,3-glucanase from Lysobacter enzymogenes encoded by the gluC gene (its catalytic domain belongs to the GH16 family), the tandem CBM domains of Pseudomonas sp. PE2 beta-1,3(4)-glucanase A (its catalytic domain also belongs to GH16), and a family 6 CBM from Cellvibrio mixtus Endoglucanase 5A (CmCBM6) which binds to the beta1,4-beta1,3-mixed linked glucans lichenan, and barley beta-glucan, cello-oligosaccharides, insoluble forms of cellulose, the beta1,3-glucan laminarin, and xylooligosaccharides, and the CBM6 of Fibrobacter succinogenes S85 XynD xylanase, appended to a GH10 domain, and Cellvibrio japonicas Cel5G appended to a GH5 (cellulase) domain. GH5 (cellulase) family includes enzymes with several known activities such as endoglucanase, beta-mannanase, and xylanase, which are involved in the degradation of cellulose and xylans. GH16 family includes enzymes with lichenase, xyloglucan endotransglycosylase (XET), and beta-agarase activities. CBM6 is an unusual CBM as it represents a chimera of two distinct binding sites with different modes of binding: binding site I within the loop regions and binding site II on the concave face of the beta-sandwich fold. For CmCBM6 it has been shown that these two binding sites have different ligand specificities.
Jiyao W et al.(2023). "The conserved domain database in 2023.",