Oligomeric structure of colicin ia channel in lipid bilayer membranes.
Colicin Ia is a soluble, harpoon-shaped bacteriocin which translocates across the periplasmic space of sensitive Escherichia coli cell by parasitizing an outer membrane receptor and forms voltage-gated ion channels in the inner membrane. This process leads to cell death, which has been thought to be caused by a single colicin Ia molecule. To directly visualize the three-dimensional structure of the channel, we generated two-dimensional crystals of colicin Ia inserted in lipid-bilayer membranes and determined a approximately 17 three-dimensional model by electron crystallography. Supported by velocity sedimentation, chemical cross-linking and single-particle image analysis, the three-dimensional structure is a crown-shaped oligomer enclosing a approximately 35 A-wide extrabilayer vestibule. Our study suggests that lipid insertion instigates a global conformational change in colicin Ia and that more than one molecule participates in the channel architecture with the vestibule, possibly facilitating the known large scale peptide translocation upon channel opening.
Greig
Sarah L
SL
From the School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Radjainia
Mazdak
M
From the School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Mitra
Alok K
AK
From the School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Electronic address: a.mitra@auckland.ac.nz.
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D002499:Centrifugation, Density Gradient; D003087:Colicins / Q000737:chemistry* / Q000302:isolation & purification; D003432:Cross-Linking Reagents / Q000737:chemistry; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000648:ultrastructure; D008051:Lipid Bilayers / Q000737:chemistry*; D008854:Microscopy, Electron; D008956:Models, Chemical; D008968:Molecular Conformation; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013395:Sucrose
D001425:Bacterial Outer Membrane Proteins; D003087:Colicins; D003432:Cross-Linking Reagents; D008051:Lipid Bilayers; D013395:Sucrose