1.C.56 The Pseudomonas syringae HrpZ Target Host Cell Membrane Cation Channel (HrpZ) Family

The Harpin-PSS (HrpZ) protein is secreted by Pseudomonas syringae via the Hrp secretion system (IIISP; TC# 3.A.6) and elicits a hypersensitive response (HR) in non-host plants upon infection and pathogenicity in hosts. It contains several repetitive regions and exhibits two extended (20 residue) regions of moderate hydrophobicity that might serve as α-helical TMSs. It is predicted to be largely of α-structure. Homologues are not found in organisms other than P. syringae.

HrpZ when inserted into liposomes and synthetic bilayers at low concentrations (2nM) provokes a cation-selective ion current with large unitary conductance. Chloride is not transported. It has been hypothesized that such channels could allow nutrient release and/or delivery of virulence factors during bacterial colonization of host plants.

The generalized transport reaction thought to be catalyzed by HrpZ is:

Small molecules (in) Small molecules (out)