Non-viral sialidases. Sialidases or neuraminidases function to bind and hydrolyze terminal sialic acid residues from various glycoconjugates, they play vital roles in pathogenesis, bacterial nutrition and cellular interactions. They have a six-bladed, beta-propeller fold with the non-viral sialidases containing 2-5 Asp-box motifs (most commonly Ser/Thr-X-Asp-[X]-Gly-X-Thr- Trp/Phe). This CD includes eubacterial and eukaryotic sialidases.
Glycosyl hydrolase families 43 and 62 form CAZY clan GH-F. This glycosyl hydrolase clan F (according to carbohydrate-active enzymes database (CAZY)) includes family 43 (GH43) and 62 (GH62). GH43 includes enzymes with beta-xylosidase (EC 3.2.1.37), beta-1,3-xylosidase (EC 3.2.1.-), alpha-L-arabinofuranosidase (EC 3.2.1.55), arabinanase (EC 3.2.1.99), xylanase (EC 3.2.1.8), endo-alpha-L-arabinanases (beta-xylanases) and galactan 1,3-beta-galactosidase (EC 3.2.1.145) activities. GH62 includes enzymes characterized as arabinofuranosidases (alpha-L-arabinofuranosidases; EC 3.2.1.55) that specifically cleave either alpha-1,2 or alpha-1,3-L-arabinofuranose side chains from xylans. GH43 are inverting enzymes (i.e. they invert the stereochemistry of the anomeric carbon atom of the substrate) that have an aspartate as the catalytic general base, a glutamate as the catalytic general acid and another aspartate that is responsible for pKa modulation and orienting the catalytic acid. Many of the enzymes in this family display both alpha-L-arabinofuranosidase and beta-D-xylosidase activity using aryl-glycosides as substrates. GH62 are also predicted to be inverting enzymes. A common structural feature of both, GH43 and GH62 enzymes, is a 5-bladed beta-propeller domain that contains the catalytic acid and catalytic base. A long V-shaped groove, partially enclosed at one end, forms a single extended substrate-binding surface across the face of the propeller.
