Folding of individual subunits of AcrB before trimerization

Abstract

AcrB and its homologous are the inner membrane components of the major multidrug transporter in Gram‐negative bacteria. In Escherichia coli, AcrB recognizes and exports a broad range of functionally and structurally unrelated substrates. The pumps confer elevated drug tolerance to bacteria, thereby increasing the difficulty to cure infections caused by these bacteria. AcrB exists and operates as a homotrimer. To investigate to what extent each individual subunit folds before they oligomerize, we created a reporter platform to detect subtle conformational changes in AcrB in vivo. We expect this thiol‐trapping based method to be generally useful in the study of many other inner membrane proteins that contain periplasmic domain. Taking advantage of this reporter platform, we created an AcrB mutant that existd as a monomer in the cell membrane. The mutant AcrB was not functional, but folded into a conformation highly resembling that of the wild type AcrB. The success in the creation of a well‐folded AcrB monomer suggests that after translation, each individual subunit folds to a conformation very similar to its final state before trimerization occurs.The work was supported by faculty start‐up fund to Wei Y. and RCTF fellowship from University of Kentucky.