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. 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. Homologues are not found in organisms other than P. syringae.
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.
Transport reaction
The generalized transport reaction thought to be catalyzed by HrpZ is:
- Small molecules (in) → Small molecules (out)
References
- 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.
- 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.
- ^ 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.
- ^ 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
- Chen, Jonathan S.; Reddy, Vamsee; Chen, Joshua H.; Shlykov, Maksim A.; Zheng, Wei Hao; Cho, Jaehoon; Yen, Ming Ren; Saier, Milton H. (2011). "Phylogenetic characterization of transport protein superfamilies: superiority of SuperfamilyTree programs over those based on multiple alignments". Journal of Molecular Microbiology and Biotechnology. 21 (3–4): 83–96. doi:10.1159/000334611. PMC 3290041. PMID 22286036.