HrpZ Family

The Pseudomonas syringae HrpZ Cation Channel (HrpZ) Family (TC# 1.C.56) is a member of the RTX-toxin superfamily. The Harpin-PSS (HrpZ; TC# 1.C.56.1.1) 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.[1] It contains several repetitive regions and exhibits two extended (20 residue) regions of moderate hydrophobicity that might serve as α-helical TMSs. The HrpZ cation channel is predicted to be largely of α-structure. HrpZ - a harpin - is a highly thermostable protein that exhibits multifunctional abilities, e.g., it elicits the hypersensitive response (HR), enhances plant growth, acts as a virulence factor, and forms pores in plant plasma membranes as well as artificial membranes.[2] Homologues are not found in organisms other than P. syringae.[3][4]

Function

When inserted into liposomes and synthetic bilayers at low concentrations (2 nM), it 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 leucine-zipper-like motifs may take part in the formation of oligomeric aggregates, and oligomerization could be related to HR elicitation.[3]

Transport Reaction

The generalized transport reaction thought to be catalyzed by HrpZ is:[4]

Small molecules (in) → Small molecules (out)

References
  1. Haapalainen, Minna; Engelhardt, Stefan; Küfner, Isabell; Li, Chun-Mei; Nürnberger, Thorsten; Lee, Justin; Romantschuk, Martin; Taira, Suvi (2011-02-01). "Functional mapping of harpin HrpZ of Pseudomonas syringae reveals the sites responsible for protein oligomerization, lipid interactions and plant defence induction". Molecular Plant Pathology. 12 (2): 151–166. doi:10.1111/j.1364-3703.2010.00655.x. ISSN 1364-3703. PMC 6640321. PMID 21199565.
  2. Choi, Min-Seon; Kim, Wooki; Lee, Chanhui; Oh, Chang-Sik (2013-10-01). "Harpins, multifunctional proteins secreted by gram-negative plant-pathogenic bacteria". Molecular Plant-Microbe Interactions. 26 (10): 1115–1122. doi:10.1094/MPMI-02-13-0050-CR. ISSN 0894-0282. PMID 23745678.
  3. Lee, J.; Klusener, B.; Tsiamis, G.; Stevens, C.; Neyt, C.; Tampakaki, A. P.; Panopoulos, N. J.; Nöller, J.; Weiler, E. W. (2001-01-02). "HrpZ(Psph) from the plant pathogen Pseudomonas syringae pv. phaseolicola binds to lipid bilayers and forms an ion-conducting pore in vitro". Proceedings of the National Academy of Sciences of the United States of America. 98 (1): 289–294. doi:10.1073/pnas.011265298. ISSN 0027-8424. PMC 14583. PMID 11134504.
  4. Saier, MH Jr. "1.C.56 The Pseudomonas syringae HrpZ Target Host Cell Membrane Cation Channel (HrpZ) Family". Transporter Classification Database. Saier Lab Bioinformatics Group / SDSC.

Further reading
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