Orientation of porin channels in the outer membrane of Bordetella pertussis |
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| Authors: | E Kocsis B L Trus A C Steven P R Smith J H Hannah M J Brennan M Kessel |
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| Institution: | Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, Maryland 20892, USA.;Computer Systems Laboratory, Division of Computer Research and Technology, National Institutes of Health, Bethesda, Maryland 20892. USA.;Department of Cell Biology, New York University Medical School, New York, New York 10016, USA.;Division of Bacterial Products, Food and Drug Administration, Bethesda, Maryland 20892, USA.;Department of Membrane and Ultrastructure Research, Hebrew University-Hadassah Medical School, Jerusalem 91-010, Israel and Department of Microbiology, University of Maryland, College Park, Maryland 20742. USA. |
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| Abstract: | We have examined the surface topography and channel connectivity of a naturally crystalline porin that is known to be functional, and whose structure has not been perturbed by detergent extraction, A three-dimensional density map, calculated from two independent tilt series of negatively stained cell envelopes, reveals three separate channels per trimer on one side (the ‘smooth’ side), and a single common opening at the other (‘rough’) side. This arrangement is consistent with the molecular structures recently determined at high resolution by X-ray crystallography for three other porins after detergent solubilization, and implies that the Bordetella pertussis porin may have the same kind of folding. Surface relief maps calculated from electron micrographs of cell envelopes contrasted by unidirectional shadowing clearly show that the side with single opening (i.e. the rough side) represents the external surface. |
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