The Cytoplasmic Domains of Membrane Protein Insertases YidC1 and YidC2 Confer Unique Structural and Functional Attributes to Each Paralog.

Integral and membrane-anchored proteins are pivotal to survival and virulence of the dental pathogen, . The bacterial chaperone/insertase, YidC, contributes to membrane protein translocation. Unlike , most Gram-positive bacteria contain two YidC paralogs. Herein, we evaluated structural features that functionally delineate YidC1 and YidC2. Bacterial YidCs contain five transmembrane domains (TMD), two cytoplasmic loops, and a cytoplasmic tail. Because YidC1 (SmYidC1) and YidC2 (SmYidC2) cytoplasmic domains (CD) are less well conserved than are TMD, we engineered ectopic expression of the 14 possible YidC1-YidC2 CD domain swap combinations. Growth and stress tolerance of each was compared to control strains ectopically expressing unmodified or . Acid and osmotic stress sensitivity are associated with deletion. Sensitivity to excess zinc was further identified as a Δ phenotype. Overall, YidC1 tolerated CD substitutions better than YidC2. Preferences toward particular CD combinations suggested potential intramolecular interactions. analysis predicted salt-bridges between C1 and C2 loops of YidC1, and C1 loop and C-terminal tail of YidC2, respectively. Mutation of contributing residues recapitulated Δ- and Δ-associated phenotypes. Taken together, this work revealed the importance of cytoplasmic domains in distinct functional attributes of YidC1 and YidC2, and identified key residues involved in interdomain interactions.