title: Identification and characterization of novel surface proteins in Lactobacillus johnsonii and Lactobacillus gasseri.
abstract: We have identified and sequenced the genes encoding the aggregation-promoting factor (APF) protein from six different strains of Lactobacillus johnsonii and Lactobacillus gasseri. Both species harbor two apf genes, apf1 and apf2, which are in the same orientation and encode proteins of 257 to 326 amino acids. Multiple alignments of the deduced amino acid sequences of these apf genes demonstrate a very strong sequence conservation of all of the genes with the exception of their central regions. Northern blot analysis showed that both genes are transcribed, reaching their maximum expression during the exponential phase. Primer extension analysis revealed that apf1 and apf2 harbor a putative promoter sequence that is conserved in all of the genes. Western blot analysis of the LiCl cell extracts showed that APF proteins are located on the cell surface. Intact cells of L. johnsonii revealed the typical cell wall architecture of S-layer-carrying gram-positive eubacteria, which could be selectively removed with LiCl treatment. In addition, the amino acid composition, physical properties, and genetic organization were found to be quite similar to those of S-layer proteins. These results suggest that APF is a novel surface protein of the Lactobacillus acidophilus B-homology group which might belong to an S-layer-like family.
authors.affiliation: Nestlé Research Center, Vers-Chez-Les-Blanc, 1000 Lausanne 26, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Ventura
authors.forename: Ivana
authors.initials: I
authors.lastname: Jankovic
authors.forename: D Carey
authors.initials: DC
authors.lastname: Walker
authors.forename: R David
authors.initials: RD
authors.lastname: Pridmore
authors.forename: Ralf
authors.initials: R
authors.lastname: Zink
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D007778:Lactobacillus / Q000737:chemistry*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000032:analysis*; D008969:Molecular Sequence Data; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C055764:S-layer proteins