title: Evidence for divalent cation (Ca2+)-stabilized oligomeric proteins and covalently bound protein-peptidoglycan complexes in the outer membrane of Rhizobium leguminosarum.
abstract: Two unusual characteristics of some outer membrane proteins of Rhizobium leguminosarum are described. First, most of the major outer membrane proteins could only be visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after lysozyme treatment of the isolated cell envelopes, suggesting a very strong, possibly covalent, interaction of these proteins with the peptidoglycan. These peptidoglycan-associated outer membrane proteins belonged to two distinct groups of immunologically related proteins, groups II and III, as defined by typing with monoclonal antibodies. As members of both groups of proteins could be radioactively labeled by growing cells in the presence of N-[3H]acetylglucosamine, we propose that variation in the apparent molecular weight of the antigens within each group is caused by varying numbers of peptidoglycan subunit residues on only two or three different outer membrane proteins. Second, group III outer membrane proteins, with masses of 35 to 46 kilodaltons, formed oligomers stabilized by divalent cations which resisted complete denaturation in 2% sodium dodecyl sulfate at 100 degrees C. Reconstitution experiments showed that of the divalent cations tested, Ca2+ and, to a lesser extent, Mn2+ and Sr2+ were the best stabilizers.
authors.affiliation: Department of Plant Molecular Biology, Leiden University, The Netherlands.
authors.forename: R A
authors.initials: RA
authors.lastname: de Maagd
authors.forename: F B
authors.initials: FB
authors.lastname: Wientjes
authors.forename: B J
authors.initials: BJ
authors.lastname: Lugtenberg
mesh_terms: D000117:Acetylglucosamine; D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000937:Antigen-Antibody Reactions; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D001435:Bacteriophages / Q000235:genetics; D002118:Calcium / Q000502:physiology*; D002413:Cations, Divalent; D002473:Cell Wall / Q000032:analysis; D004492:Edetic Acid; D006358:Hot Temperature; D009113:Muramidase; D010457:Peptidoglycan / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D012231:Rhizobium / Q000032:analysis* / Q000254:growth & development / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D002413:Cations, Divalent; D010457:Peptidoglycan; D004492:Edetic Acid; D009113:Muramidase; D002118:Calcium; D000117:Acetylglucosamine