Differential complementation of ΔtolA Escherichia coli by a Yersinia enterocolitica TolA homologue

The Tol system is an interactive set of envelope proteins that includes both outer and cytoplasmic membrane proteins. Central to this system is TolA, which spans the periplasmic space to communicate with residents of each membrane. To identify motifs involved in the protein/protein interactions through which TolA acts, the ability of a phylogenetically distinct TolA protein from Yersinia enterocolitica to function in the Tol system of Escherichia coli was examined. Although at least 59 codons shorter and only c . 67% identical to its E. coli homologue, the Y. enterocolitica gene encoded a protein that supported the physiological function of the Tol system in E. coli , and conferred sensitivity to the TolA-dependent colicins A, K, and E1, but interestingly, not to colicin N. The correlation of conferred phenotype with sequence similarities and differences provides a first step in defining essential structural motifs and their specific contributions to function.