Porin B is a porin from Corynebacterium glutamicum which allows the exchange of material across the mycolic acid layer which is the protective nonpolar barrier. Porin B has an alpha helical core structure consisting of four alpha-helices surrounding a nonpolar interior. There is a disulphide bridge between helices 1 and 4 to form a stable covalently bound ring [1]. The channel of PorB is oligomeric [1].

1: A putative alpha-helical porin from Corynebacterium glutamicum. Ziegler K, Benz R, Schulz GE; J Mol Biol. 2008;379:482-491. PMID:18462756