InterPro domain: IPR023614

Porins are found in the outer membranes of Gram-negative bacteria,mitochondria and chloroplasts, where they form ion-selective channels forsmall hydrophilic molecules (up to ~600 D) [ 1 , 2 ]. X-ray structureanalyses of several bacterial porins [ 3 , 4 , 5 ] have revealed a large 16-strandedanti-parallel beta-barrel structure enclosing the transmembrane pore, bycontrast with all other integral membrane proteins described to date,which are alpha-helical. Three subunits form a trimer; the 3-fold axis isapproximately parallel to the barrel axes and is assumed to beperpendicular to the membrane plane.

From the range of porins now known, similarities have been observed betweenporins from different species, and between porins of different specificitywithin the same species. But most porins cannot be related to each other onthe basis of sequence alone, and this is reflected in the lengths of theknown porin sequences, which range from 282-483 residues/monomer.

This superfamily represents the structural domain found in porins.

1. Biophysics of the structure and function of porins. Q. Rev. Biophys. 23, 367-403
2. Porins and specific channels of bacterial outer membranes. Mol. Microbiol. 6, 435-42
3. The structure of porin from Rhodobacter capsulatus at 1.8 A resolution. FEBS Lett. 280, 379-82
4. A common channel-forming motif in evolutionarily distant porins. J. Struct. Biol. 107, 136-45
5. Refined structure of the porin from Rhodopseudomonas blastica. Comparison with the porin from Rhodobacter capsulatus. J. Mol. Biol. 243, 891-905