Oral Presentation The 3rd Prato Conference on Pore Forming Proteins 2015

It was commonly believed that cell walls of Gram-positive bacteria do not represent any permeability barrier and do not contain pore-forming proteins. Members of the phylum: Actinobacteria within the order: Corynebacteriales and the family: Corynebacteriaceae form a noticeable exception within this rule. These organisms contain in addition to the peptidoglycan layer, large amounts of lipids in their cell wall. Major constituents are the mycolic acids covalently linked to the arabinogalactan and free lipid associated with the mycolic acid layer. Many species within this group of mycolic acid containing bacteria are known either because of their medical or biotechnological relevance. The mycolata comprises microorganisms, which cause dangerous infections worldwide such as Mycobacterium tuberculosis (TBC, 3 millions deaths/a), Mycobacterium leprae (lepra), Nocardia farcinica (nocardiosis) and Corynebacterium diphtheriae (diphtheria) and those used producing amino acids on industrial scale such as Corynebacterium glutamicum and Corynebacterium efficiens (glutamate production; worldwide about 340.000 t/a). Within the last twenty years, we investigated the cell walls of Mycobacteriae, Nocardiae, Dietziae, Rhodococci and Corynebacteriae species for the presence of cell wall channels. To date many cell wall channels were identified in the family Corynebacteriaceae. These cell wall channels are either mostly cation‑selective or rarely anion-selective. They are water-filled with diameters around 1.4‑2.4 nm and many of them contain point charges. They are found in members of the mycolata but they have quite diverse primary or secondary structures, probably related to length of the mycolic acids. In addition, they all form either hetero- or homooligomers with molecular masses between 5 and 20 kDa. The big homo‑oligomeric complex of the cell wall channel of Mycobacterium smegmatis is an octamer of 20 kDa formed by ß-strands. Other cell wall channels, in particular those from Corynebacteriae and Rhodococci have molecular masses between 5‑8 kDa and are presumably formed by α-helices.