Coupling site-directed mutagenesis with high-level expression: large scale production of mutant porins from<i>E. coli</i>

Combination of an origin repair mutagenesis system with a new mutS host strain increased the efficiency of mutagenesis from 46% to 75% mutant clones. Overexpression with the T7 expression system afforded large quantities of proteins from mutant strains. A series of E. coli BE host strains devoid of major outer membrane proteins was constructed, facilitating the purification of mutant porins to homogeneity. This allowed preparation of 149 porin mutants in E. coli used in detailed explorations of the structure and function of this membrane protein to high resolution.