title: Staphylococcal major autolysin (Atl) is involved in excretion of cytoplasmic proteins.
abstract: Many microorganisms excrete typical cytoplasmic proteins into the culture supernatant. As none of the classical secretion systems appears to be involved, this type of secretion was referred to as "nonclassical protein secretion." Here, we demonstrate that in Staphylococcus aureus the major autolysin plays a crucial role in release of cytoplasmic proteins. Comparative secretome analysis revealed that in the wild type S. aureus strain, 22 typical cytoplasmic proteins were excreted into the culture supernatant, although in the atl mutant they were significantly decreased. The presence or absence of prophages had little influence on the secretome pattern. In the atl mutant, secondary peptidoglycan hydrolases were increased in the secretome; the corresponding genes were transcriptionally up-regulated suggesting a compensatory mechanism for the atl mutation. Using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a cytoplasmic indicator enzyme, we showed that all clinical isolates tested excreted this protein. In the wall teichoic acid-deficient tagO mutant with its increased autolysis activity, GAPDH was excreted in even higher amounts than in the WT, confirming the importance of autolysis in excretion of cytoplasmic proteins. To answer the question of how discriminatory the excretion of cytoplasmic proteins is, we performed a two-dimensional PAGE of cytoplasmic proteins isolated from WT. Surprisingly, the most abundant proteins in the cytoplasm were not found in the secretome of the WT, suggesting that there exists a selection mechanism in the excretion of cytoplasmic proteins. As the major autolysin binds at the septum site, we assume that the proteins are preferentially released at and during septum formation.
authors.affiliation: Department of Microbial Genetics, University of Tübingen, D-72076 Tübingen, Germany.
authors.forename: Linda
authors.initials: L
authors.lastname: Pasztor
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Ziebandt
authors.forename: Mulugeta
authors.initials: M
authors.lastname: Nega
authors.forename: Martin
authors.initials: M
authors.lastname: Schlag
authors.forename: Sabine
authors.initials: S
authors.lastname: Haase
authors.forename: Mirita
authors.initials: M
authors.lastname: Franz-Wachtel
authors.forename: Johannes
authors.initials: J
authors.lastname: Madlung
authors.forename: Alfred
authors.initials: A
authors.lastname: Nordheim
authors.forename: David E
authors.initials: DE
authors.lastname: Heinrichs
authors.forename: Friedrich
authors.initials: F
authors.lastname: Götz
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D003593:Cytoplasm / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013203:Staphylococcal Infections / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000472:pathogenicity
chemical_list: D001426:Bacterial Proteins; D012333:RNA, Messenger; D009238:N-Acetylmuramoyl-L-alanine Amidase