Mutational analysis of a transmembrane segment in a bacterial chemoreceptor

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The Trg receptor in Escherichia coli mediates chemotaxis.
• Its transmembrane domain is crucial for signal transduction.
• Previous studies using cysteine scanning had limited success in identifying key residues.

Purpose of the Study:

• To identify critical residues in the TM2 segment of the Trg receptor.
• To elucidate the mechanism of transmembrane signaling.
• To understand the structural basis of receptor function.

Main Methods:

• Random mutagenesis and screening of the Trg receptor's TM2 segment.
• In vivo signaling assays.
• Analysis of single-residue substitutions and their functional impact.

Main Results:

• Identified 42 single-residue substitutions altering Trg receptor function, with 16 having drastic effects.
• Defined a functionally important helical face of TM2, oriented towards the protein interior.
• Substitutions specifically altered transmembrane signaling, with some reducing and others inducing signaling.
• Demonstrated significant tolerance for substitutions, including charged residues, within the transmembrane domain.

Conclusions:

• Conformational signaling involves TM2 movement relative to TM1.
• Optimal signaling requires stable interactions between homologous helices at the transmembrane interface.
• The Trg receptor exhibits remarkable tolerance for mutations in its transmembrane segments.