The 1.55 Å resolution structure of Nicotiana alata SF11-RNase associated with gametophytic self-incompatibility

Abstract

The crystal structure of Nicotiana alata (ornamental tobacco) SF11-RNase, an S-allelic glycoprotein associated with gametophytic self-incompatibility, was determined by X-ray diffraction at 1.55 Å resolution. The protein has a tertiary structure typical of members of the RNase T2 family as it consists of a variant of the (α + β) fold and has eight helices and seven strands. A heptasaccharide moiety is also present, and amino acid residues that serve as the catalytic acid and base can be assigned to His32 and His91, respectively. Two "hypervariable" regions, known as HVa and HVb, are the proposed sites of S-allele discrimination during the self-incompatibility reaction, and in the SF11-RNase ..