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. 2019 Mar 29;7(2):10.1128/microbiolspec.psib-0024-2018. doi: 10.1128/microbiolspec.psib-0024-2018

FIGURE 3.

FIGURE 3

Two models for FhaB secretion: distal N-terminus versus hairpin. In the model proposed by Coutte et al. (38) (A), the N terminus of FhaB is pushed away from the membrane as more of the polypeptide translocates through FhaC. The protease SphB1 cleaves between the mature C-terminal domain (MCD) and the periplasmic prodomain, causing release of FHA. In the alternative “hairpin” model proposed by Mazar and Cotter (34) (B), the N terminus of FhaB remains bound to FhaC during secretion, and the MCD is located at the distal end of the β-helix. A portion of the MCD spans the helix length, as it is tethered to the periplasmic prodomain. The prodomain N terminus (PNT) prevents translocation of the prodomain through FhaC.