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. Author manuscript; available in PMC: 2020 Aug 1.
Published in final edited form as: Protein J. 2019 Aug;38(4):389–408. doi: 10.1007/s10930-019-09862-3

Fig. 3. Schematics of Class II assembly pathways.

Fig. 3.

Type 2 secretion systems elaborate ‘pseudopili’ on an IM platform. They recruit substrates delivered across the IM via the GSP or Tat systems to the tip of the pseudopilus, which might act as a piston to export the substrate through the secretin channel to the cell surface. T4Ps are phylogenetically and functionally related to the T2SSs, except they build pili that dynamically extend and retract through the coordinated actions of the GspE and PilT ATPases. Type 9 secretion systems recruit substrates from the periplasm through binding of conserved C-terminal domains (CTDs). Some substrates are covalently bound to the cell surface via a ‘sortase’ like mechanism.