Membrane fusion activity of purified SipB, a Salmonella surface protein essential for mammalian cell invasion

• Published in: Molecular microbiology Vol. 37; no. 4; pp. 727 - 739
• Main Authors: Hayward, Richard D., McGhie, Emma J., Koronakis, Vassilis
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.08.2000; Blackwell Publishing Ltd
• Subjects: Amino Acid Sequence; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacterial Proteins - physiology; Escherichia coli; HeLa Cells; Humans; Hydrogen-Ion Concentration; macropinocytosis; membrane fusion; Membrane Fusion - physiology; Membrane Lipids - metabolism; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Membrane Proteins - physiology; Molecular Sequence Data; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Salmonella; Salmonella typhimurium - pathogenicity; SipB protein
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2000.02027.x

An early event in Salmonella infection is the invasion of non‐phagocytic intestinal epithelial cells. The pathogen is taken up by macropinocytosis, induced by contact‐dependent delivery of bacterial proteins that subvert signalling pathways and promote cytoskeletal rearrangement. SipB, a Salmonella protein required for delivery and invasion, was shown to localize to the cell surface of bacteria invading mammalian target cells and to fractionate with outer membrane proteins. To investigate the properties of SipB, we purified the native full‐length protein following expression in recombinant Escherichia coli. Purified SipB assembled into hexamers via an N‐terminal protease‐resistant domain predicted to form a trimeric coiled coil, reminiscent of viral envelope proteins that direct homotypic membrane fusion. The SipB protein integrated into both mammalian cell membranes and phospholipid vesicles without disturbing bilayer integrity, and it induced liposomal fusion that was optimal at neutral pH and influenced by membrane lipid composition. SipB directed heterotypic fusion, allowing delivery of contents from E. coli‐derived liposomes into the cytosol of living mammalian cells.