title: MscL of Bacillus subtilis prevents selective release of cytoplasmic proteins in a hypotonic environment.
abstract: Bacillus subtilis serves as an excellent model to study protein secretion at a proteomic scale. Most of the extracellular proteins are exported from the cytoplasm via the secretory (Sec) pathway. Despite extensive studies, the secretion mechanisms of about 25% of the extracellular proteins are unknown. This suggests that B. subtilis makes use of alternative mechanisms to release proteins into its environment. In search for novel pathways, which contribute to biogenesis of the B. subtilis exoproteome, we investigated a possible role of the large conductance mechanosensitive channel protein MscL. We compared protein secretion by MscL deficient and proficient B. subtilis cells. MscL did not contribute to secretion under standard growth conditions. Unexpectedly, we discovered that under hypo-osmotic shock conditions specific, normally cytoplasmic proteins were released by mscL mutant cells. This protein release was selective since not all cytoplasmic proteins were equally well released. We established that this protein release by mscL mutant cells cannot be attributed to cell death or lysis. The presence of MscL, therefore, seems to prevent the specific release of cytoplasmic proteins by B. subtilis during hypo-osmotic shock. Our unprecedented findings imply that an unidentified system for selective release of cytoplasmic proteins is active in B. subtilis.
authors.affiliation: Department of Medical Microbiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Thijs R H M
authors.initials: TR
authors.lastname: Kouwen
authors.forename: Haike
authors.initials: H
authors.lastname: Antelmann
authors.forename: René
authors.initials: R
authors.lastname: van der Ploeg
authors.forename: Emma L
authors.initials: EL
authors.lastname: Denham
authors.forename: Michael
authors.initials: M
authors.lastname: Hecker
authors.forename: Jan Maarten
authors.initials: JM
authors.lastname: van Dijl
mesh_terms: D017209:Apoptosis; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000235:genetics / Q000502:physiology*; D050296:Microbial Viability; D008856:Microscopy, Fluorescence; D009154:Mutation; D009997:Osmotic Pressure / Q000502:physiology; D040901:Proteomics; D055571:Secretory Pathway / Q000235:genetics / Q000502:physiology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001426:Bacterial Proteins; D007473:Ion Channels