The functional properties of Ompβ, the regularly arrayed porin of the hyperthermophilic bacterium Thermotoga maritima

Abstract The regularly arrayed outer membrane protein, Ompβ, of Thermotoga maritima was purified to homogeneity and was characterized functionally by incorporation into artificial lipid bilayers. The polypeptide has an apparent molecular mass ( M _r) of approx. 40 000 and forms stable trimers in the presence of 1% octyl-polyoxyethylene or 2% SDS which dissociate when boiling the sample. The protein has a secondary structure (predominantly β-sheet) and an amino acid composition characteristic for porins. Pore-forming activity was demonstrated by porin incorporation into artificial bilayers proving that Ompβ is a true porin: selectivity measurements showed a 4.4-fold selectivity for cations over anions. Conductivity of the porin is influenced by surface charges and also depends on the applied voltage.