title: Three oligopeptide-binding proteins are involved in the oligopeptide transport of Streptococcus thermophilus.
abstract: The functions necessary for bacterial growth strongly depend on the features of the bacteria and the components of the growth media. Our objective was to identify the functions essential to the optimum growth of Streptococcus thermophilus in milk. Using random insertional mutagenesis on a S. thermophilus strain chosen for its ability to grow rapidly in milk, we obtained several mutants incapable of rapid growth in milk. We isolated and characterized one of these mutants in which an amiA1 gene encoding an oligopeptide-binding protein (OBP) was interrupted. This gene was a part of an operon containing all the components of an ATP binding cassette transporter. Three highly homologous amiA genes encoding OBPs work with the same components of the ATP transport system. Their simultaneous inactivation led to a drastic diminution in the growth rate in milk and the absence of growth in chemically defined medium containing peptides as the nitrogen source. We constructed single and multiple negative mutants for AmiAs and cell wall proteinase (PrtS), the only proteinase capable of hydrolyzing casein oligopeptides outside the cell. Growth experiments in chemically defined medium containing peptides indicated that AmiA1, AmiA2, and AmiA3 exhibited overlapping substrate specificities, and that the whole system allows the transport of peptides containing from 3 to 23 residues.
authors.affiliation: Unité de Biochimie et Structure des Protéines, Institut National de la Recherche Agronomique, 78352 Jouy en Josas cedex, France.
authors.forename: Peggy
authors.initials: P
authors.lastname: Garault
authors.forename: Dominique
authors.initials: D
authors.lastname: Le Bars
authors.forename: Colette
authors.initials: C
authors.lastname: Besset
authors.forename: Veronique
authors.initials: V
authors.lastname: Monnet
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D003470:Culture Media; D008074:Lipoproteins / Q000502:physiology*; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D013291:Streptococcus / Q000254:growth & development / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D003470:Culture Media; D008074:Lipoproteins; D011135:Polysaccharides, Bacterial; C098632:exopolysaccharide, Streptococcus; C046506:oligopeptide-binding protein, bacteria