PorH, a new channel-forming protein present in the cell wall of Corynebacterium efficiens and Corynebacterium callunae

Corynebacterium callunae and Corynebacterium efficiens are close relatives of the glutamate-producing mycolata species Corynebacterium glutamicum. The properties of the pore-forming proteins, extracted by organic solvents, were studied. The cell extracts contained channel-forming proteins that formed ion-permeable channels with a single-channel conductance of about 2 to 3 nS in 1 M KCI in a lipid bilayer assay. The corresponding proteins from both corynebacteria were purified to homogeneity and were named PorH and PorH. Electrophysiological studies of the channels suggested that they are wide and water-filled. Channels formed by PorH are cation-selective, whereas PorH forms slightly anion-selective channels. Both proteins were partially sequenced. A multiple sequence alignment search within the known chromosome of C. efficiens demonstrated that it contains a gene that fits the partial amino acid sequence of PorH. PorH shows high homology to PorH. PorH is encoded in the bacterial chromosome by a gene that is localized within the vicinity of the porA gene of C. efficiens. PorH has no signal sequence at the N terminus, which means that it is not exported by the Sec-secretion pathway. The structure of PorH in the cell wall of the corynebacteria is discussed. © 2005 SGM.