Figure 2.

Model of the type II secretion pathway in Gram-negative bacteria. (a) The T2SS-dependent exoproteins, shown as yellow circles, are first exported across the IM via the Sec (purple) or Tat (brown) machineries. The exoproteins are subsequently recognized and transported across the OM by the secreton (blue/green). (b) Schematic of the secreton divided into three sub-complexes. Secretin GspD_Q (blue) forms a dodecameric pore in the OM through its C-terminal domain whilst its N-terminal part protrudes in the periplasm. The IM surface, composed of T2SS proteins F_S, L_Y and M_Z, and the traffic ATPase GspE_R are coloured green. Secretin is connected to the IM surface through the transperiplasmic protein GspC_P (blue/green). The pseudopilus, mostly constituted by the GspG_T major pseudopilin and capped by the minor pseudopilins GspH_U, I_V, J_W and K_X quaternary complex, is shown in orange and red. Gsp proteins are indicated by their corresponding letter.