PMID: 12835321 , Related PDB id: 1UGL

Authors:

Mishima M, Takayama S, Sasaki K, Jee JG, Kojima C, Isogai A, Shirakawa M

Title:

Structure of the male determinant factor for Brassica self-incompatibility.

Journal:

J Biol Chem. 2003 Sep 19;278(38):36389-95. Epub 2003 Jun 30.

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.