Dissecting structure/function relationship of Streptococcus mutans membrane protein chaperones/insertases, YidC1 and YidC2

Abstract

BackgroundApproximately, one third of most bacterial open reading frames encode membrane proteins; therefore, understanding the machinery that translocates these proteins to their functional location is of great interest. Most membrane proteins are translocated co‐translationally by the signal recognition particle (SRP) pathway via the SecYEG translocon. Additionally the Oxa/Alb/YidC (mitochondria/chloroplast/bacteria) family of membrane‐localized protein chaperone/insertases assists in membrane protein translocation in a Sec‐dependent manner, or independently if the proteins are small with two or fewer transmembrane (TM) domains. Most gram‐negative bacteria contain a single yidC whose deletion is lethal. Most gram‐positive bacteria contain two or more YidCs. The cariogenic bacterium S. mutans encodes YidC1 and YidC2, each with similar 5 TM domain topologies. Deletion of yidC2 results in a severe phenotype similar to disruption of the SRP pathway including impaired growth, sensitivity to acid, osmotic, and oxidative stresses, and loss of competence and mutacin production. Deletion of DyidC1 leads to increased localization of surface proteins and hyperadherence. The goal of this study is to better understand the structure and function of YidC1 and YidC2 as related to their known phenotypes.MethodsThe significance of the two cytoplasmic loops, C1 and C2, of YidC1 and YidC2 were evaluated in domain swapping experiments in which DNA segments encoding one or both C1 and C2 domains of yidC1 were incorporated into yidC2 and vice versa. Chimeric genes were integrated into the non‐essential gtfA locus of the DyidC1 and DyidC2 strains. Next the residual endogenous yidC was deleted, thus generating strains with a sole chimeric YidC for phenotypic analyses. In addition, a naturally‐acquired W138R point mutation within yidC1 was identified in a phenotypically‐reverted DyidC2 mutant; therefore, the significance of this residue was evaluated as well.Results and ConclusionsAn S. mutans strain producing a chimeric YidC2 harboring the C1 loop of YidC1 was similar to the DyidC2 strain with respect to sensitivity to acid and osmotic stress suggesting a functional contribution of YidC2's C1 loop to stress tolerance. Transfer of YidC2 C1 into YidC1 enabled YidC1 to rescue acid and osmotic stress sensitivity. Also, a deliberately engineered W138R point mutation within YidC1 enabled it to rescue growth and stress phenotypes of the DyidC2 mutant. Sequence comparison revealed that the YidC1 tryptophan 138 residue corresponds to serine 152 in YidC2, the only polar residue within its TM3. Additionally, engineered W138K/S mutations within YidC1 also enabled rescue of DyidC2‐associated phenotypes. These data reveal that functional activities unique to YidC2 reside within both its C1 domain and TM3 that can be transferred to YidC1.Support or Funding InformationNIH grant: R01 DE08007This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.