2.A.116 The Peptidoglycolipid Addressing Protein (GAP) Family The cell envelope of mycobacteria is a complex multilaminar structure that protects the cell from stresses encountered in the environment. The outermost layer of the mycobacterial envelope typically contains species-specific glycolipids. Depending on the mycobacterial species, the major glycolipid localized at the surface can be either a phenolglycolipid or a peptidoglycolipid (GPL). Six genes in Mycobacterium smegmatis involved in GPLs synthesis are clustered in a single genomic region of approximately 60 kb. A small integral membrane protein of 272 amino acids named GAP (GAP: GPL Addressing Protein) is specifically required for the transport of the GPLs to the cell surface (Sonden et al. 2005). This protein is predicted to contain six transmembrane segments and possesses homologues across the mycobacterial genus, thus delineating a new protein family. This GAP family represents a new paradigm for the transport of lipids across the mycobacterial envelope. The mechanism of its action is not known, but this family has been shown to be a member of the LsyE superfamily. Therefore, these proteins are probably secondary carriers. The generalized reaction catalyzed by members of the GAP family is: PGL (in) → PGL (outer membrane)
This family belongs to the LysE Superfamily.
References:
Sondén, B., D. Kocíncová, C. Deshayes, D. Euphrasie, L. Rhayat, F. Laval, C. Frehel, M. Daffé, G. Etienne, and J.M. Reyrat. (2005). Gap, a mycobacterial specific integral membrane protein, is required for glycolipid transport to the cell surface. Mol. Microbiol. 58: 426-440.
Examples:
TC#	Name	Organismal Type	Example
2.A.116.1.1	*The peptidoglycolipid exporter, GAP (Sondén et al., 2005).*	Actinobacteria	GAP of Mycobacterium smegmatis (AAT01808)

2.A.116.1.2	Gap homologue of 237 aas	Actinobacteria	Gap of Mycobacterium tuberculosis

2.A.116.1.3	Gap homologue of 225 aas	Actinobacteria	Gap homologue of Streptomyces hydroscopicus

2.A.116.1.4	Gap homologue of 223 aas	Actinobacteria	Gap homologue of Microlunatus phosphovorus

2.A.116.1.5	Gap homologue of 213 aas	Actinobacteria	Gap homologue of Catenulispora acidiphila

2.A.116.1.6	Gap homologue of 232 aas	Euryarchaea	Gap homologue of Methanobacterium formicicum

2.A.116.1.7	Gap homologue of 216 aas	Actinobacteria	Gap homologue of Gordonia rhizosphera

Examples:
TC#	Name	Organismal Type	Example
2.A.116.2.1	Gap homologue of 228 aas	Cyanobacteria	Gap homologue of Cyanobium gracile

2.A.116.2.2	Gap homologue of 229 aas	Cyanobacteria	Gap homologue of Prochlorococcus marinus

Examples:
TC#	Name	Organismal Type	Example
2.A.116.3.1	Gap homologue of 260 aas	Actinobacteria	Gap homologue of Arthrobacter arilaitensis

2.A.116.3.2	Gap homologue of 229 aas	Actinobacteria	Gap homologue of Nocardiopsis alba

2.A.116.3.3	Gap homologue of 218 aas	Firmicutes	Gap homologue of Bacillus cereus

2.A.116.3.4	Hypothetical protein of 237 aas	Firmicutes	HP of Clostridium cellulolyticus