Charge Composition Features of Model Single-span Membrane Proteins That Determine Selection of YidC and SecYEG Translocase Pathways in Escherichia coli*□S

Background: Proteins generally require the YidC and SecYEG machineries for membrane insertion. Results: The specific features of membrane protein sequences determine YidC/SecYEG requirements for insertion. Conclusion: The charge composition of membrane proteins determines the YidC and Sec translocase requirements in E. coli. Significance: Translocase requirements for membrane insertion are determined by the charge composition of membrane proteins. Wehave investigated the features of single-spanmodelmem-brane proteins based upon leader peptidase that determines whether the proteins insert by a YidC/Sec-independent, YidC-only, or YidC/Sec mechanism. We find that a protein with a highly hydrophobic transmembrane segment that inserts into themembrane by aYidC/Sec-independentmechanismbecomes YidC-dependent if negatively charged residues are inserted into the translocated periplasmic domain or if the hydrophobicity of the transmembrane segment is reduced by substituting polar residues for nonpolar ones. This suggests that charged residue