title: Cadaverine covalently linked to peptidoglycan is required for interaction between the peptidoglycan and the periplasm-exposed S-layer-homologous domain of major outer membrane protein Mep45 in Selenomonas ruminantium.
abstract: The peptidoglycan of Selenomonas ruminantium is covalently bound to cadaverine (PG-cadaverine), which likely plays a significant role in maintaining the integrity of the cell surface structure. The outer membrane of this bacterium contains a 45-kDa major protein (Mep45) that is a putative peptidoglycan-associated protein. In this report, we determined the nucleotide sequence of the mep45 gene and investigated the relationship between PG-cadaverine, Mep45, and the cell surface structure. Amino acid sequence analysis showed that Mep45 is comprised of an N-terminal S-layer-homologous (SLH) domain followed by α-helical coiled-coil region and a C-terminal β-strand-rich region. The N-terminal SLH domain was found to be protruding into the periplasmic space and was responsible for binding to peptidoglycan. It was determined that Mep45 binds to the peptidoglycan in a manner dependent on the presence of PG-cadaverine. Electron microscopy revealed that defective PG-cadaverine decreased the structural interactions between peptidoglycan and the outer membrane, consistent with the proposed role for PG-cadaverine. The C-terminal β-strand-rich region of Mep45 was predicted to be a membrane-bound unit of the 14-stranded β-barrel structure. Here we propose that PG-cadaverine possesses functional importance to facilitate the structural linkage between peptidoglycan and the outer membrane via specific interaction with the SLH domain of Mep45.
authors.affiliation: Department of Microbial Biotechnology, Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.forename: Kyong-Cheol
authors.initials: KC
authors.lastname: Ko
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Takatsuka
authors.forename: Naoki
authors.initials: N
authors.lastname: Abe
authors.forename: Jun
authors.initials: J
authors.lastname: Kaneko
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Itoh
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kamio
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002103:Cadaverine / Q000737:chemistry*; D002462:Cell Membrane / Q000648:ultrastructure; D002473:Cell Wall / Q000648:ultrastructure; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020357:Selenomonas / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D010457:Peptidoglycan; D002103:Cadaverine