title: URF13, a ligand-gated, pore-forming receptor for T-toxin in the inner membrane of cms-T mitochondria.
abstract: URF13 is the product of a mitochondrial-encoded gene (T-urf13) found only in maize plants containing the Texas male-sterile cytoplasm (cms-T), and it is thought to be responsible for both cytoplasmic male sterility and the susceptibility of cms-T maize to the fungal pathogens Bipolaris maydis race T and Phyllosticata maydis. Mitochondria isolated from cms-T maize are uniquely sensitive to pathotoxins (T-toxin) produced by these fungi and to methomyl (a commercial insecticide). URF13 acts as a receptor that specifically binds T-toxin to produce hydrophilic pores in the inner mitochondrial membrane. When expressed in Escherichia coli cells, URF13 also forms hydrophilic pores in the plasma membrane if exposed to T-toxin or methomyl. Topological studies established that URF13 contains three membrane-spanning alpha-helices, two of which are amphipathic and can contribute to pore formation. Chemical cross-linking of URF13 was used to demonstrate the existence of URF13 oligomers in cms-T mitochondria and E. coli cells. The ability of the carboxylate-specific reagent, N,N'-dicyclohexycarbodiimide, to cross-link URF13 was used in conjunction with site-directed mutagenesis to establish that the URF13 tetramer has a central core consisting of a four-alpha-helical bundle which undergoes a conformational change after interaction with T-toxin or methomyl. Overall, the experimental evidence indicates that URF13 functions as a ligand-gated, pore-forming T-toxin receptor in cms-T mitochondria.
authors.affiliation: Department of Botany/Developmental, Cell, and Molecular Biology Group, Duke University, Durham, North Carolina 27708-1000, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Rhoads
authors.forename: C S
authors.initials: CS
authors.lastname: Levings
authors.forename: J N
authors.initials: JN
authors.lastname: Siedow
mesh_terms: D000595:Amino Acid Sequence; D004272:DNA, Mitochondrial / Q000378:metabolism; D017343:Genes, Plant; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D024101:Mitochondrial Proteins; D008961:Models, Structural; D008969:Molecular Sequence Data; D009183:Mycotoxins / Q000378:metabolism*; D010935:Plant Diseases; D018515:Plant Leaves; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D012098:Reproduction; D003313:Zea mays / Q000378:metabolism*
chemical_list: D004272:DNA, Mitochondrial; D024101:Mitochondrial Proteins; D009183:Mycotoxins; D010940:Plant Proteins; C071393:URF13 protein, Zea mays