PROSITE documentation PDOC51909 [for PROSITE entry PS51909]

Invertebrate (I)-type lysozyme domain profile

Lysozyme (EC 3.2.1.17) is an ubiquitous enzyme and is widely distributed in a range of phylogenetically diverse organisms from bacteriophage to humans. Lysozyme is mainly involved in the innate immune system and protection of host against microbial infection. The mechanism of lysozyme in killing bacteria is by hydrolyzing the β-1,4-glycosidic linkages between N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG) of peptidoglycan (PG), which is a layer in the bacterial cell wall. Based on differences in amino acid sequences, catalytic characteristic, and original sources, lysozymes are classified into chicken (C)-type (see <PDOC00119>), goose (G)-type, virus (V)-type, lambda (L)-type, chalaropsis (Ch)-type (see <PDOC00737>), plant (P)-type and invertebrate (I)-type. I-type lysozymes have been identified in phylogenetically diverse organisms, including mollusca, nematoda, annelida, arthropoda and echinodermata. I-type lysozymes play an important role in immunity and digestion in invertebrates and are usually regarded as the first barrier against pathogens. The I-type lysozyme has multiple activities. For its muramidase activity, it is identified as lysozyme; for its isopeptidase activity, it is named destabilase; chitinase and non-enzymatic antibacterial activities are also manifested [1,2,3,4,5]. They belong to the glycosyl hydrolase 22 (GH22) family [E1].

The I-type lysozyme domain is characterized by six α-helices and one β-sheet (see <PDB:2DQA>). It contains 14 cysteines that all form disulfide bonds (C1-C12, C2-C14, C3-C4, C5-C6, C7-C10, C8-C9, C11-C13). The catalytic residues are a glutamate in the α1-helix and an aspartate in the β1-strand [6,7].

The profile we developed covers the entire I-type lysozyme domain.