Fig. 1.

Variation of environmental pH for plant pathogen P. syringae effector proteins translocated via the T3SS and His residues in the structured core of AvrPto. (A) The T3SS supramolecular assembly spans across both bacterial membranes, the apoplast, and the host cell wall. Effector proteins first encounter the mildly acidic bacterial cytoplasm, must then at least partially unfold for translocation through the narrow pilus, and then must refold upon delivery to the neutral host cytoplasm. (B) Seven His residues are dispersed across the TrAvrPto structure; the lone Trp residue is buried at the center of the helix bundle.