The Type II secretion system, also called Secretion-dependent pathway (SDP), is responsible for the transport of proteins across the outer membrane first exported to the periplasm by the Sec or Tat translocon in Gram-negative (diderm) bacteria [1,2]. The T2SG family includes proteins such as EpsG (P45773) in Vibrio cholera, XcpT also called PddA (Q00514) in Pseudomonas aeruginosa or PulG (P15746)in Klebsiella pneumoniae. The PulG is thought to be anchored in the inner membrane with its C-terminus directed towards the periplasme [3]. Together with other members of the Type II secretion machinery, it is thought to assemble into a pilus-like structure that may function as a dynamic mechanism to push secreted proteins out of the cell. The polypeptide is organized into a long N-terminal alpha-helix followed by a loop region that separates it from a C-terminal anti-parallel beta-sheet [1].

1: Structure and assembly of the pseudopilin PulG. Kohler R, Schafer K, Muller S, Vignon G, Diederichs K, Philippsen A, Ringler P, Pugsley AP, Engel A, Welte W; Mol Microbiol 2004;54:647-664. PMID:15491357

2: Protein secretion in Pseudomonas aeruginosa: characterization of seven xcp genes and processing of secretory apparatus components by prepilin peptidase. Bally M, Filloux A, Akrim M, Ball G, Lazdunski A, Tommassen J; Mol Microbiol 1992;6:1121-1131. PMID:1588814

3: Five additional genes in the pulC-O operon of the gram-negative bacterium Klebsiella oxytoca UNF5023 which are required for pullulanase secretion. Reyss I, Pugsley AP; Mol Gen Genet 1990;222:176-184. PMID:2129543

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

5: 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

6: 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