Poster Presentation 2014 International Biophysics Congress

Role of a unique arginine residue on the assembly of the translocator domain in a trimeric autotransporter (#301)

Eriko Aoki 1 , Riki Hisata 1 , Kazuo Fujiwara 1 , Masamichi Ikeguchi 1
  1. Department of Bioinfomatics, Soka University, Hachioji, Japan

Haemophilus influenzae adhesin (Hia) belongs to trimeric autotransporter family. The autotransporter consists of a passenger domain, which is a virulence factor, and a translocator domain, which is embedded in the outer membrane. The crystal structure of Hia translocator domain (HiaT) has shown that HiaT forms a transmembrane β-barrel of 12 β-strands, four of which are provided from each subunit. The β-barrel has a pore that is traversed by three α-helices, one of which is provided from each subunit. This protein has a unique arginine residue at 1077. Arg1077 side chains from three subunits protrude from the β-strand toward the center of the barrel and are close to each other. This residue is positioned at the C-terminus of the helix and considered to neutralize the helix dipole. To investigate role of this residue on the trimer assembly and stability, we replaced this arginine with the neutral amino acid, methionine, and the properties of the mutant were investigated. Both HiaT and the mutant were dissociated by formic-acid treatment, and they were able to reassemble in the presence of detergent. Although the mutation increased the rate of reassembly, the fraction of correctly reassembled protein is decreased. These results suggest that the repulsion between positively charged arginines may be important for efficient folding even though it reduces the rate of the assembly.