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glycoside hydrolase family 55 (GH55) family domains and similar proteins This family includes glycoside hydrolase family 55 (GH55) domains, which contains both endo- (EC 3.2.1.39) and exo-beta-1,3-glucanases (EC 3.2.1.58), based on the hydrolysis position. These enzymes hydrolyze beta-1,3-glucan bonds via inversion of stereochemistry at the anomeric carbon. GH55 is also called laminarinase due to its ability to hydrolyze laminarin, a beta-1,3-glucan with occasional beta-1,6 branching, found in brown algae such as Laminaria digitata. They have also been shown to react with the beta-1,3-glucans from fungal and plant cell walls. Also included in this family is SacteLam55A from the highly cellulolytic Streptomyces sp. SirexAA-E, a secreted protein encoded by SACTE_4363. Structural studies reveal an extended substrate-binding cleft with six or more subsites for sugar binding formed at the interface of two right handed beta-helical domains. Mutation studies support a critical glutamate as a catalytic acid and a proton relay network that activates water to serve as the catalytic base. Trichoderma harzianum and T. viride LamA1 have been characterized as endo-acting enzymes while Phanerochaete chrysosporium Lam55A, Chaetomium thermophilum CtLam55, as well as SacteLam55A, are exo-acting enzymes. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",