InterPro: IPR002152 Glycoside hydrolase, family 23

O-Glycosyl hydrolases EC:3.2.1. are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [1, 2, 3]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site [4]. Because the fold of proteins is better conserved than their sequences, some of the families can be grouped in clans.

Anser sp. (goose)-type lysozyme (lysozyme G) hydrolyses 1,4-beta-linkages between N-acetyl-D-glucosamine and N-acetylmuramic acid in peptidoglycan hetero-polymers of prokaryote cell walls. Lysozyme G shows preference for N-acetylmuramic acid residues that are substituted with a peptide moiety; it acts only as a glycanohydrolase.

The structure of goose egg-white lysozyme (GEWL) with a bound trisaccharide has been refined to 1.6A resolution [5]. The trisaccharide occupies analogous sites to the B, C and D subsites of chicken (HEWL) and Bacteriophage T4 (T4L) lysozymes. All of these enzymes display the same characteristic hydrogen bonding pattern between protein and substrate [5]. Glu73 of GEWL corresponds closely to Glu35 of HEWL (Glu11 of T4L), supporting the view that this group is critical to the catalytic mechanism. However, lysozyme G has no obvious counterpart to Asp52 of chicken lysozyme (Asp20 in T4L), suggesting that a second acidic residue is not essential for its catalytic activity, and may not be required for the activity of other lysozymes. The structure of GEWL belongs to the mainly alpha class, its sequence showing no discernible similarity to other lysozymes. The enzyme has been classified as belonging to family 23 of glycosyl hydrolases [6, 3] (GH23).