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J Membr Biol. 2000 Jun 1;175(3):165-80.

Families of proteins forming transmembrane channels.

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  • 1Department of Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA.


Channel-forming proteins/peptides fall into over 100 currently recognized families, most of which are restricted to prokaryotes or eukaryotes, but a few of which are ubiquitous. These proteins fall into three major currently recognized classes: (i) alpha-helix-type channels present in bacterial, archaeal and eukaryotic cytoplasmic and organellar membranes, (ii) beta-barrel-type porins present in the outer membranes of Gram-negative bacterial cells, mitochondria and chloroplasts, and (iii) protein/peptide toxins targeted to the cytoplasmic membranes of cells other than those that synthesize the toxins. High-resolution 3-dimensional structural data are available for representative proteins/peptides of all three of these channel-forming types. Each type exhibits distinctive features that distinguish them from the other channel protein types and from carriers. Structural, functional, and evolutionary aspects of transmembrane channel-formers are discussed.

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