Functional Overlap but Lack of Complete Cross-Complementation of Streptococcus mutans and Escherichia coli YidC Orthologs

Department of Oral Biology, University of Florida, P. O. Box 100424, Gainesville, FL 32610; Department of Chemistry, The Ohio State University, Columbus, OH 43210, USA; Department of Physiology, Department of Microbiology, Immunology and Medical Genetics, Molecular Biology Institute, University of California, Los Angeles, CA 90095

^* To whom correspondence should be addressed. Email: dalbey{at}chemistry.ohio-state.edu. jbrady{at}dental.ufl.edu.

	Abstract

Oxa/YidC/Alb family proteins are chaperones involved in membrane protein insertion and assembly. Streptococcus mutans encodes two YidC paralogs. Elimination of yidC2, but not yidC1, results in stress-sensitivity with decreased membrane-associated F₁F₀ ATPase activity and an inability to initiate growth at low pH or high salt (Hasona A. et al., 2005, PNAS 102, 17466). We now show that Escherichia coli YidC complements for acid-, and partially for salt-, tolerance in S. mutans lacking yidC2 and S. mutans YidC1 or YidC2 complements growth in liquid medium, restores the proton motive force, and functions to assemble the F₁F₀ ATPase in a previously engineered E.coli YidC-depletion strain (Samuelson, J. 2000, Nature 406, 637). Both YidC1 and YidC2 also promote membrane insertion of known YidC substrates in E coli; however, complete membrane integrity is not fully replicated as evidenced by induction of phage shock protein A. While both function to rescue E. coli growth in broth, a different result is observed on agar plates whereby growth of the YidC-depletion strain is largely restored by 247YidC2, a hybrid S. mutans YidC2 fused to the YidC targeting region, but not by a similar chimera 247YidC1, nor by YidC1 or YidC2. Simultaneous expression of YidC1 and YidC2 improves complementation on plates. This study demonstrates functional redundancy between gram-negative and gram-positive YidC orthologs, but also highlights differences in their activity depending on growth conditions and species background suggesting that the complete functional spectrum of each is optimized for the specific bacteria and environment in which they reside.