Peptidoglycan-associated outer membrane protein Mep45 of rumen anaerobe Selenomonas ruminantium forms a non-specific diffusion pore via its C-terminal transmembrane domain.
The major outer membrane protein Mep45 of Selenomonas ruminantium, an anaerobic Gram-negative bacterium, comprises two distinct domains: the N-terminal S-layer homologous (SLH) domain that protrudes into the periplasm and binds to peptidoglycan, and the remaining C-terminal transmembrane domain, whose function has been unknown. Here, we solubilized and purified Mep45 and characterized its function using proteoliposomes reconstituted with Mep45. We found that Mep45 forms a nonspecific diffusion channel via its C-terminal region. The channel was permeable to solutes smaller than a molecular weight of roughly 600, and the estimated pore radius was 0.58 nm. Truncation of the SLH domain did not affect the channel property. On the basis of the fact that Mep45 is the most abundant outer membrane protein in S. ruminantium, we conclude that Mep45 serves as a main pathway through which small solutes diffuse across the outer membrane of this bacterium.
a Frontier Research Institute for Interdisciplinary Sciences , Tohoku University , Sendai , Japan.|b Graduate School of Life Sciences , Tohoku University , Sendai , Japan.
Seiji
S
Kojima
c Graduate School of Agricultural Science , Tohoku University , Sendai , Japan.
Kanako
K
Hayashi
b Graduate School of Life Sciences , Tohoku University , Sendai , Japan.
Saeko
S
Tochigi
b Graduate School of Life Sciences , Tohoku University , Sendai , Japan.
Tomonobu
T
Kusano
c Graduate School of Agricultural Science , Tohoku University , Sendai , Japan.
Jun
J
Kaneko
c Graduate School of Agricultural Science , Tohoku University , Sendai , Japan.|d Graduate School of Comprehensive Human Sciences , Shokei-Gakuin University , Natori , Japan.
Yoshiyuki
Y
Kamio
D000693:Anaerobiosis; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004058:Diffusion; D008565:Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000072417:Protein Domains; D055550:Protein Stability; D012417:Rumen / Q000382:microbiology*; D020357:Selenomonas / Q000378:metabolism*; D012995:Solubility
D001426:Bacterial Proteins; D008565:Membrane Proteins
Gram-negative bacteria; channel; outer membrane; porin; rumen