Stabilising and destabilising modifications of cysteines in the E. coli outer membrane porin protein OmpC

Three sulfhydryl labels were used to modify two mutated sites, R37C and R74C in the eyelet of the outer membrane porin OmpC. Modification of R37C with the neutral groups Aldrithiol and bimane increases thermal stability but the negatively charged iodoacetate causes a decrease in thermal stability. The effects of substitution at R74C were less significant. Bimane labelling increases the voltage sensitivity and decreases the single channel conductance at R37C asymmetrically with smaller channels being recorded at cis negative voltages. Negatively charged acetate does not affect the voltage gating.