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. 2020 Dec 15;9:e62816. doi: 10.7554/eLife.62816

Figure 7. Model depicting the role of Eag chaperones and prePAAR in type VI secretion.

Figure 7.

(A) PAAR proteins exist with or without prePAAR domains. Those that lack prePAAR (orphan), can interact with VgrG and form a functional T6SS spike complex without any additional factors. By contrast, prePAAR-containing effectors contain multiple domains (evolved) and likely require the prePAAR motif for proper folding of the PAAR domain and thus, loading onto the T6SS apparatus. (B) prePAAR-containing effectors can be divided into two classes: class I effectors have a single TMD and contain a C-terminal toxin domain that is likely housed within a Rhs cage whereas class II effectors contain two TMDs and do not possess a Rhs cage. TMD-chaperone and prePAAR-PAAR interactions are required for effector stability and VgrG interaction, respectively, for both classes of prePAAR effectors. (C) Depiction of a prePAAR-containing effector being exported by the T6SS into recipient cells. Inset shows the hydrophobic TMDs of a class II prePAAR effector disrupting the inner membrane of the target bacterium to allow entry of the effector toxin domain into the cytoplasm.