title: alpha-Macroglobulins are present in some gram-negative bacteria: characterization of the alpha2-macroglobulin from Escherichia coli.
abstract: alpha-Macroglobulins (alphaMs) are large glycoproteins that have been identified in a wide range of vertebrate and invertebrate species and are mostly thiol ester containing proteinase inhibitors. A recent analysis of bacterial genomes ( Budd, A., Blandin, S., Levashina, E. A., and Gibson, T. J. (2004) Genome Biol. 5, R38 ) identified many alpha-macroglobulin-like sequences that appear to have been acquired by Gram-negative bacteria from their metazoan hosts. We report the first expression and characterization of such a bacterial alpha-macroglobulin, that from Escherichia coli. This is also the first alpha-macroglobulin to be characterized that is predicted to be membrane-anchored. We found that the 183-kDa protein contains an intact thiol ester, is monomeric, and is localized to the periplasmic space. Reaction with proteinase results in limited cleavage within a bait region, rapid activation of the thiol ester, cross-linking to the attacking proteinase or other available nucleophiles, and partial protection of the proteinase against macromolecular substrates. Given these properties and the co-occurrence of the alphaM gene with one for a repair transglycosylase, this suggests a possible role for bacterial alphaMs in cell defense following host attack. Such a role would make bacterial alphaMs appropriate novel targets for antibiotic drugs.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
authors.forename: Ninh
authors.initials: N
authors.lastname: Doan
authors.forename: Peter G W
authors.initials: PG
authors.lastname: Gettins
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism*; D004952:Esters / Q000737:chemistry; D006090:Gram-Negative Bacteria / Q000378:metabolism*; D006801:Humans; D019272:Leukocyte Elastase / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D013050:Spectrometry, Fluorescence / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013438:Sulfhydryl Compounds / Q000737:chemistry; D000511:alpha-Macroglobulins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D004952:Esters; D013438:Sulfhydryl Compounds; D000511:alpha-Macroglobulins; D019272:Leukocyte Elastase