Glycoside hydrolase, family 22, lysozyme (IPR000974)

Short name: Glyco_hydro_22_lys

Overlapping homologous superfamilies

Family relationships


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 [PMID: 7624375, PMID: 8535779]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site.

Glycoside hydrolase family 22 GH22 comprises enzymes with two known activities; lysozyme type C (EC: and alpha-lactalbumins. Asp and/or the carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base.

Lysozyme is a muramidase that hydrolyses beta-1,4-links between N-acetyl- muramic acid and N-acetyl-D-glucosamine in the peptidoglycan of bacterial cell walls [PMID: 3413092], thus helping to fight invading bacteria. In this capacity, the enzyme is found in tears and saliva, but it has also been recruited for a digestive role in the true stomach (abomasum) of ruminants and colobine monkeys: here it probably degrades the cell walls of bacteria passing from the foregut, allowing the breakdown products to be digested by other stomach enzymes [PMID: 3120013, PMID: 2738070]. The stomach form of lysozyme is endowed with special physiochemical properties that allow it to function in an acidic and protease-rich environment.

Lysozyme C is similar to alpha-lactalbumin in terms of primary sequence and structure [PMID: 6715332], and both have probably evolved from a common ancestral protein. There is, however, no similarity in function, lactalbumin being involved in the formation of lactose and is essential for milk production. Another significant difference between the two enzymes is that while all lactalbumins have the ability to bind calcium, this property is restricted to only a few lysozymes [PMID: 3666156].

From human testis cDNA libraries, a group of lysozyme c-like sequences is identified [PMID: 21676251, PMID: 24013621]. The function of this group of lysozyme c-like proteins is not clear. Some of them (LYZL2, SLLP1/SPACA3/LYXL3, LYZL4 and LYZL6) are expressed in the male reproductive tract [PMID: 12606493, PMID: 16014814] and may be involved in fertilisation.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0003796 lysozyme activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.