title: Structure of the male determinant factor for Brassica self-incompatibility.
abstract: Many flowering plants possess a self-incompatibility system to prevent inbreeding. In Brassica rapa, self/non-self recognition in mating is established through S-haplotype-specific interactions between stigma receptors and S-locus protein 11 (SP11, also called S-locus cysteine-rich protein) that is encoded at the highly polymorphic S-locus. Here we describe the solution structure of the SP11 protein of the S8-haplotype (S8-SP11), which specifically binds to the stigma factor of the same haplotype. It folds into an alpha/beta sandwich structure that resembles those of plant defensins. Residues important for structural integrity are highly conserved among the allelic SP11s, suggesting the existence of a common folding pattern. Structure-based sequence alignment and homology modeling of allelic SP11 identified a hyper-variable (HV) region, which is thought to form a loop that bulges out from the body of the protein that is amenable to solvent exposure. We suggest that the HV region could serve as a specific binding site for the stigma receptor.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Mishima
authors.forename: Seiji
authors.initials: S
authors.lastname: Takayama
authors.forename: Kei-Ichi
authors.initials: K
authors.lastname: Sasaki
authors.forename: Jun-Goo
authors.initials: JG
authors.lastname: Jee
authors.forename: Chojiro
authors.initials: C
authors.lastname: Kojima
authors.forename: Akira
authors.initials: A
authors.lastname: Isogai
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shirakawa
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001665:Binding Sites; D001937:Brassica / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006239:Haplotypes; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000502:physiology*; D018514:Plant Structures / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D008024:Ligands; D010940:Plant Proteins; C431526:SP11 protein, Brassica