Chapter 17 The porin superfamily: diversity and common features

Abstract

Publisher Summary This chapter discusses the diversity and common features of the porin superfamily. The name porin was first used by Taiji Nakae in 1976 to describe a class of oligomeric proteins from the outer membrane of Gram-negative bacteria which “form aqueous pores and penetrate through the thickness of the membrane in reconstituted vesicles as well as in native outer membrane, thus conferring hydrophilic permeability to that membrane.” Currently, three porin structures known are: one at high resolution 1.8 A; Rhodobacter capsulatus; and two at moderate resolution OmpF and PhoE porins from E. Coli at 2.4 and 3.0 A resolutions, respectively. Transmembrane segments of pore-forming proteins are often not predicted with the hydrophobicity analysis alone because some pieces of secondary structure in pore-forming proteins are amphipathic. They have one hydrophilic face towards the lumen of the pore and one hydrophobic face towards either lipid or protein.