This family consists of Type II secretion system protein L sequences from several Gram-negative (diderm) bacteria. The Type II secretion system, also called Secretion-dependent pathway (SDP), is responsible for extracellular secretion of a number of different proteins, including proteases and toxins. This pathway supports secretion of proteins across the cell envelope in two distinct steps, in which the second step, involving translocation through the outer membrane, is assisted by at least 13 different gene products. T2SL is predicted to contain a large cytoplasmic domain represented by this family and has been shown to interact with the autophosphorylating cytoplasmic membrane protein T2SE. It is thought that the tri-molecular complex of T2SL, T2SE (Pfam:PF00437) and T2SM (Pfam:PF04612) might be involved in regulating the opening and closing of the secretion pore and/or transducing energy to the site of outer membrane translocation [1].

1: Direct interaction of the EpsL and EpsM proteins of the general secretion apparatus in Vibrio cholerae. Sandkvist M, Hough LP, Bagdasarian MM, Bagdasarian M; J Bacteriol 1999;181:3129-3135. PMID:10322014

2: The structure of the cytoplasmic domain of EpsL, an inner membrane component of the type II secretion system of Vibrio cholerae: an unusual member of the actin-like ATPase superfamily. Abendroth J, Bagdasarian M, Sandkvist M, Hol WG; J Mol Biol 2004;344:619-633. PMID:15533433

3: The general secretory pathway: a general misnomer?. Desvaux M, Parham NJ, Scott-Tucker A, Henderson IR; Trends Microbiol. 2004;12:306-309. PMID:15223057

4: Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella. Peabody CR, Chung YJ, Yen MR, Vidal-Ingigliardi D, Pugsley AP, Saier MH Jr; Microbiology. 2003;149:3051-3072. PMID:14600218

5: Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. Desvaux M, Hebraud M, Talon R, Henderson IR; Trends Microbiol. 2009;17:139-145. PMID:19299134