InterPro: IPR001724 Glycoside hydrolase, family 58

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.

Family 58 (GH58) includes the endo-N-acetyl-neuraminidases (EC:3.2.1.129). Phage E specifically recognises and infects strains of Escherichia coli that display the alpha-2,8-linked polysialic acid K1 capsule [5, 6]. phage E endosialidase is thought to be responsible for initial absorption of the phage to the host bacterium [5]. The native enzyme is probably a trimer of identical 74kDa subunits. Within the K1E endosialidase sequence, a central region of 500 amino acids shows 84% identity to K1F endosialidase [5]. Both enzymes contain two copies of a sialidase sequence motif common to many bacterial and viral sialidases. These motifs flank the region of greatest identity between the two endosialidases, suggesting that this domain is involved in binding and hydrolysis of the polysialic acid substrate [5].