title: Serum amyloid A protein binds to outer membrane protein A of gram-negative bacteria.
abstract: Serum amyloid A (SAA) is the major acute phase protein in man and most mammals. We observed SAA binding to a surprisingly large number of Gram-negative bacteria, including Escherichia coli, Salmonella typhimurium, Shigella flexneri, Klebsiella pneumoniae, Vibrio cholerae, and Pseudomonas aeruginosa. The binding was found to be high affinity and rapid. Importantly, this binding was not inhibited by high density lipoprotein with which SAA is normally complexed in serum. Binding was also observed when bacteria were offered serum containing SAA. Ligand blots following SDS-PAGE or two-dimensional gels revealed two major ligands of 29 and 35 kDa that bound SAA when probing with radiolabeled SAA or SAA and monoclonal anti-SAA. Following fractionation the ligand was found in the outer membrane fraction of E. coli and was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry to be outer membrane protein A (OmpA). OmpA-deficient E. coli did not bind SAA, and following purification of OmpA the protein retained binding activity. The ligands on other bacteria were likely to be homologues of OmpA because wild type, but not OprF-deficient, P. aeruginosa bound SAA.
authors.affiliation: Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom.
authors.forename: Ranjeeta
authors.initials: R
authors.lastname: Hari-Dass
authors.forename: Chandrabala
authors.initials: C
authors.lastname: Shah
authors.forename: David J
authors.initials: DJ
authors.lastname: Meyer
authors.forename: John G
authors.initials: JG
authors.lastname: Raynes
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D005434:Flow Cytometry; D006090:Gram-Negative Bacteria / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000378:metabolism; D008024:Ligands; D008075:Lipoproteins, HDL / Q000737:chemistry; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D012486:Salmonella typhimurium / Q000378:metabolism; D000685:Serum Amyloid A Protein / Q000096:biosynthesis*; D012763:Shigella flexneri / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014734:Vibrio cholerae / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008024:Ligands; D008075:Lipoproteins, HDL; D011994:Recombinant Proteins; D000685:Serum Amyloid A Protein; C078167:OMPA outer membrane proteins