Bacterial alpha-L-rhamnosidase 6 hairpin glycosidase domain. This family consists of bacterial rhamnosidase A and B enzymes. L-Rhamnose is abundant in biomass as a common constituent of glycolipids and glycosides, such as plant pigments, pectic polysaccharides, gums or biosurfactants. Some rhamnosides are important bioactive compounds. For example, terpenyl glycosides, the glycosidic precursor of aromatic terpenoids, act as important flavouring substances in grapes. Other rhamnosides act as cytotoxic rhamnosylated terpenoids, as signal substances in plants or play a role in the antigenicity of pathogenic bacteria.
Carbohydrate Binding Module 6 (CBM6); appended mainly to glycoside hydrolase (GH) family 16 alpha- and beta agarases. This family includes carbohydrate binding module 6 (CBM6) domains that are appended mainly to glycoside hydrolase (GH) family 16 agarases. These CBM6s are non-catalytic carbohydrate binding domains that facilitate the activity of alpha- and beta-agarase catalytic modules which are involved in the hydrolysis of 1,4-beta-D-galactosidic linkages. These CBM6s bind specifically to the non-reducing end of agarose chains, recognizing only the first repeat of the disaccharide, and directing the appended catalytic modules to areas of the plant cell wall attacked by beta-agarases. 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. This family includes three tandem CBM6s from the Saccharophagus degradans agarase Aga86E, and three tandem CBM6s from Vibrio sp. strain PO-303 AgaA; in both these proteins these are appended to a GH16 domain. Vibrio AgaA also contains a Big-2-like protein-protein interaction domain. This family also includes two tandem CBM6s from an endo-type beta-agarase from a deep-sea Microbulbifer-like isolate, which are appended to a GH16 domain, and two of three CBM6s of Alteromonas agarilytica AgaA alpha-agarase, which are appended to a GH96 domain.