title: Identification of extracellular surface-layer associated proteins in Lactobacillus acidophilus NCFM.
abstract: Bacterial surface (S-) layers are crystalline arrays of self-assembling, proteinaceous subunits called S-layer proteins (Slps), with molecular masses ranging from 40 to 200 kDa. The S-layer-forming bacterium Lactobacillus acidophilus NCFM expresses three major Slps: SlpA (46 kDa), SlpB (47 kDa) and SlpX (51 kDa). SlpA has a demonstrated role in adhesion to Caco-2 intestinal epithelial cells in vitro, and has been shown to modulate dendritic cell (DC) and T-cell functionalities with murine DCs. In this study, a modification of a standard lithium chloride S-layer extraction revealed 37 proteins were solubilized from the S-layer wash fraction. Of these, 30 have predicted cleavage sites for secretion, 24 are predicted to be extracellular, six are lipid-anchored, three have N-terminal hydrophobic membrane spanning regions and four are intracellular, potentially moonlighting proteins. Some of these proteins, designated S-layer associated proteins (SLAPs), may be loosely associated with or embedded within the bacterial S-layer complex. Lba-1029, a putative SLAP gene, was deleted from the chromosome of L. acidophilus. Phenotypic characterization of the deletion mutant demonstrated that the SLAP LBA1029 contributes to a pro-inflammatory TNF-α response from murine DCs. This study identified extracellular proteins and putative SLAPs of L. acidophilus NCFM using LC-MS/MS. SLAPs appear to impart important surface display features and immunological properties to microbes that are coated by S-layers.
authors.affiliation: Department of Microbiology, North Carolina State University, Raleigh, NC, USA.
authors.forename: Brant
authors.initials: B
authors.lastname: Johnson
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Selle
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: O'Flaherty
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, USA.
authors.forename: Yong Jun
authors.initials: YJ
authors.lastname: Goh
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, USA.|Department of Microbiology, North Carolina State University, Raleigh, NC, USA.
authors.forename: Todd
authors.initials: T
authors.lastname: Klaenhammer
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D003713:Dendritic Cells / Q000187:drug effects; D007779:Lactobacillus acidophilus / Q000737:chemistry* / Q000276:immunology; D013058:Mass Spectrometry; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000276:immunology; D051379:Mice; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D008562:Membrane Glycoproteins; C055764:S-layer proteins; D014409:Tumor Necrosis Factor-alpha