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1.D.3 The Channel-Forming Syringopeptin (Syringopeptin) Family

Syringopeptins represent a family of related lipodepsipeptide phytotoxins produced by strains of Pseudomonas syringae. The structures of syringopeptin forms SP22 and SP25 are known. The fatty acid can be either 3-hydroxydecanoate or 3-hydroxydodecanoate. Non-protein amino acids present in these toxins include: 2,4-diaminobutyrate, 2,3-dehydroaminobutyrate, allothreonine, and D-amino acids. The structures of both forms (SP22 and SP25) are presented in Bender et al. (1999). Additional isoforms have been identified.

Syringopeptin exhibits similarity to syringomycin in structure, mode of action, and physiological consequences to the plant. For example, it may induce H+:K+ exchange after forming oligomeric pores in the plant plasma membrane, but it can also facilitate Ca2+ entry into the plant cell cytoplasm. It is homolytic and forms ion channels in artificial membranes. This activity causes it to exhibit a spectrum of antimicrobial activities distinct from those of syringomycin. Thus some bacteria are killed by syringopeptin but not syringomycin, while others exhibit the reverse sensitivity. These antibiotics are probably both secreted by an ABC transporter, SyrD of P. syringae.

The generalized transport reaction catalyzed by syringopeptins is:

cations (in) cations (out)

References associated with 1.D.3 family:

Bender, C.L., F. Alarcòn-Chaidez, and D.C. Gross. (1999). Pseudomonas syringaephytotoxins: mode of action, regulation, and biosynthesis by peptide and polyketide synthetases. Microbiol. Mol. Biol. Rev. 63: 266-292. 10357851