Activated chemoreceptor arrays remain intact and hexagonally packed

Area of Science:

• Microbiology
• Cell Biology
• Biophysics

Background:

• Bacterial chemoreceptors form ordered arrays crucial for sensitive signal transduction.
• The precise conformational changes driving signal transduction within these arrays remain poorly understood.
• Existing hypotheses propose large structural rearrangements or even array disassembly upon activation, but evidence is conflicting.

Purpose of the Study:

• To investigate the structural dynamics of bacterial chemoreceptor arrays during signal transduction.
• To determine if array organization changes significantly upon attractant binding or in mutant strains mimicking different signaling states.

Main Methods:

• Utilized electron cryotomography (cryo-ET) to visualize chemoreceptor arrays in Caulobacter crescentus.
• Analyzed array structure in cells under various growth conditions and immediately after attractant exposure.
• Examined array structure in cheB and cheR deletion mutants simulating pre-adaptation signaling states.

Main Results:

• Chemoreceptor arrays consistently displayed a 12 nm hexagonal packing arrangement across different media conditions.
• Array size and other structural parameters remained constant regardless of growth conditions or immediate attractant exposure.
• Mutants mimicking attractant- or repellent-bound states also exhibited the same stable lattice structure.

Conclusions:

• Bacterial chemoreceptor arrays do not undergo large-scale disassembly or significant packing changes upon activation.
• Signal transduction and amplification are likely mediated by subtle, nanoscale conformational alterations within the stable array structure.
• These findings resolve conflicting reports and establish a model for signal transduction based on conserved array organization.