Release of the type I secreted alpha-haemolysin via outer membrane vesicles from Escherichia coli.
The alpha-haemolysin is an important virulence factor commonly expressed by extraintestinal pathogenic Escherichia coli. The secretion of the alpha-haemolysin is mediated by the type I secretion system and the toxin reaches the extracellular space without the formation of periplasmic intermediates presumably in a soluble form. Surprisingly, we found that a fraction of this type I secreted protein is located within outer membrane vesicles (OMVs) that are released by the bacteria. The alpha-haemolysin appeared very tightly associated with the OMVs as judged by dissociation assays and proteinase susceptibility tests. The alpha-haemolysin in OMVs was cytotoxically active and caused lysis of red blood cells. The OMVs containing the alpha-haemolysin were distinct from the OMVs not containing alpha-haemolysin, showing a lower density. Furthermore, they differed in protein composition and one component of the type I secretion system, the TolC protein, was found in the lower density vesicles. Studies of natural isolates of E. coli demonstrated that the localization of alpha-haemolysin in OMVs is a common feature among haemolytic strains. We propose an alternative pathway for the transport of the type I secreted alpha-haemolysin from the bacteria to the host cells during bacterial infections.
Balsalobre
Carlos
C
Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden. cbalsalobre@ub.edu
Silván
Jose Manuel
JM
Berglund
Stina
S
Mizunoe
Yoshimitsu
Y
Uhlin
Bernt Eric
BE
Wai
Sun Nyunt
SN
D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000166:cytology / Q000378:metabolism* / Q000472:pathogenicity; D004927:Escherichia coli Infections; D029968:Escherichia coli Proteins / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D006367:HeLa Cells; D006460:Hemolysin Proteins / Q000378:metabolism*; D006801:Humans; D026901:Membrane Transport Proteins
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D005227:Fatty Acids; D006460:Hemolysin Proteins; D026901:Membrane Transport Proteins; C073126:tolC protein, E coli