This domain is found in the non-catalytic carbohydrate binding module 65B (CMB65B) present in Eubacterium cellulosolvens. CBMs are present in plant cell wall degrading enzymes and are responsible for targeting, which enhances catalysis. CBM65s display higher affinity for oligosaccharides, such as cellohexaose, and particularly polysaccharides than cellotetraose, which fully occupies the core component of the substrate binding cleft. The concave surface presented by beta-sheet 2 comprises the beta-glucan binding site in CBM65s. C6 of all the backbone glucose moieties makes extensive hydrophobic interactions with the surface tryptophans of CBM65s. Three out of the four surface Trp are highly conserved. The conserved metal ion site typical of CBMs is absent in this CBM65 family [1].

1: Understanding how noncatalytic carbohydrate binding modules can display specificity for xyloglucan. Luis AS, Venditto I, Temple MJ, Rogowski A, Basle A, Xue J, Knox JP, Prates JA, Ferreira LM, Fontes CM, Najmudin S, Gilbert HJ; J Biol Chem. 2013;288:4799-4809. PMID:23229556