The structure of porin from Paracoccus denitrificans at 3.1 A resolution

The crystal structure of a non-specific porin from Paracoccus denitrificans at 3.1 A resolution has been solved by molecular replacement using the porin from Rhodopseudomonas blastica as the search model. Paracoccus porin is very similar to other non-specific porins of known structure: a trimer of 16 stranded beta-barrels each with a central pore constricted by a long extracellular loop folding back against the barrel wall. The distinctive distribution of charged residues of this non-specific porin contributes to understanding the relation between structure and ion selectivity.