Mapping the interactions between Escherichia coli TolQ transmembrane segments.

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• The tolQRAB-pal operon is conserved in Gram-negative bacteria.
• TolQRA proteins form an inner membrane complex regulating outer membrane lipoprotein interactions.
• Proton-motive force drives TolQR regulation of TolA conformation.

Purpose of the Study:

• To define the organization of TolQ's three transmembrane helices (TMHs).
• To elucidate the multimerization mechanism of TolQ within the Tol-Pal complex.

Main Methods:

• Construction of epitope-tagged TolQ variants.
• Immunodetection of in vivo and in vitro chemically cross-linked TolQ.
• Cysteine-scanning mutagenesis to probe helix interactions.

Main Results:

• TolQ exists as multimers within the inner membrane complex.
• Cysteine substitutions suggest a dynamic model for TolQ helix interactions.
• The hairpin of the last two TolQ TMHs changes conformation, while the first TMH forms intramolecular interactions.

Conclusions:

• TolQ multimerization is crucial for the Tol-Pal complex function.
• A dynamic model explains TolQ's structural organization and interactions.
• Understanding TolQ's TMH organization provides insights into bacterial envelope biogenesis.