Abstract
Corynebacterium jeikeium, a resident of human skin, is often associated with multidrug resistant nosocomial infections in immunodepressed patients. C. jeikeium K411 belongs to mycolic acid-containing actinomycetes, the mycolata and contains a channel-forming protein as judged from reconstitution experiments with artificial lipid bilayer experiments. The channel-forming protein was present in detergent treated cell walls and in extracts of whole cells using organic solvents. A gene coding for a 40 amino acid long polypeptide possibly responsible for the pore-forming activity was identified in the known genome of C. jeikeium by its similar chromosomal localization to known porH and porA genes of other Corynebacterium strains. The gene jk0268 was expressed in a porin deficient Corynebacterium glutamicum strain. For purification temporarily histidine-tailed or with a GST-tag at the N-terminus, the homogeneous protein caused channel-forming activity with an average conductance of 1.25 nS in 1M KCl identical to the channels formed by the detergent extracts. Zero-current membrane potential measurements of the voltage dependent channel implied selectivity for anions. This preference is according to single-channel analysis caused by some excess of cationic charges located in the channel lumen formed by oligomeric alpha-helical wheels. The channel has a suggested diameter of 1.4 nm as judged from the permeability of different sized hydrated anions using the Renkin correction factor. Surprisingly, the genome of C. jeikeium contained only one gene coding for a cell wall channel of the PorA/PorH type found in other Corynebacterium species. The possible evolutionary relationship between the heterooligomeric channels formed by certain Corynebacterium strains and the homooligomeric pore of C. jeikeium is discussed.
Highlights
Members of the genus Corynebacterium are of considerable interest because some are potent producers of glutamate, lysine and other amino acids through fermentation processes on an industrial scale
We extended the search for cell wall channels to the C. jeikeium strain K411 that is a clinical isolate with a known genome [39]
We present in this study the characterization of the first homooligomeric channelforming protein of the PorA type of a strain within the genus Corynebacterium, which is formed in contrast to other cell wall channels from the mycolata by alpha-helical stretches
Summary
Members of the genus Corynebacterium are of considerable interest because some are potent producers of glutamate, lysine and other amino acids through fermentation processes on an industrial scale. Long mycolic acids have been found in Mycobacteria 60–90 carbon atoms), but they are short in Corynebacteria (22–38 carbon atoms) [12,13,14,15,16] This means that the cell wall of the mycolata forms a permeability barrier and probably has the same function as the outer membrane of gramnegative bacteria. We present in this study the characterization of the first homooligomeric channelforming protein of the PorA type of a strain within the genus Corynebacterium, which is formed in contrast to other cell wall channels from the mycolata by alpha-helical stretches. A phylogenic tree suggests that PorACj could be the ancestor of all known PorA/H proteins from Corynebacterium strains
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