This subfamily includes VirB1 protein, one of twelve proteins making up type IV secretion systems (T4SS). T4SS are macromolecular assemblies generally composed of VirB1-11 and VirD4 proteins, and are used by bacteria to transport material across their membranes. VirB1 acts as a lytic transglycosylase (LT), and is important with respect to piercing the peptidoglycan layer in the periplasm. LTs catalyze the cleavage of the beta-1,4-glycosidic bond between N-acetylmuramic acid (MurNAc) and N-acetyl-D-glucosamine (GlcNAc) as do "goose-type" lysozymes. However, in addition to this, they also make a new glycosidic bond with the C6 hydroxyl group of the same muramic acid residue. Proteins similar to this family include the soluble and insoluble membrane-bound LTs in bacteria, the LTs in bacteriophage lambda, as well as the eukaryotic "goose-type" lysozymes (goose egg-white lysozyme; GEWL).
Jiyao W et al.(2023). "The conserved domain database in 2023.",