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J Mol Biol. 1999 Jan 29;285(4):1347-51.

Voltage and pH-induced channel closure of porin OmpF visualized by atomic force microscopy.

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M. E. Müller-Institute for Microscopy, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.


Gram-negative bacteria are protected by an outer membrane in which trimeric channels, the porins, facilitate the passage of small solutes. The pores are formed by membrane-spanning antiparallel beta-strands, which are connected by short turns on the periplasmic side and long loops on the extracellular side. Voltage and pH-dependent conformational changes of these extracellular loops have now been visualized by atomic force microscopy of two-dimensional crystals of Escherichia coli porin OmpF. The observed conformational changes accompany the closure of the channel entrance, and suggest that this is a mechanism that the cells have evolved to protect themselves from drastic changes of the environment.

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