Selective Detection of a Key Region in Chemotaxis Signaling Protein Complexes by Solid-State NMR.

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Large protein complexes are crucial for biological processes but difficult to study.
• Bacterial chemotaxis receptor signaling complexes are >500 kDa and assemble into hexagonal arrays.
• Understanding protein dynamics in native states is essential for elucidating function.

Purpose of the Study:

• To apply solid-state NMR (SSNMR) to investigate the structure and dynamics of bacterial chemotaxis receptor signaling complexes.
• To selectively probe rigid regions within the >500 kDa complex.
• To identify conformational changes associated with different signaling states.

Main Methods:

• Utilized ¹³C-¹⁵N dipolar coupling-based SSNMR experiments.
• Optimized in vitro assembly methods for homogeneous, active complexes.
• Employed dynamics-based NMR spectral editing to isolate rigid protein regions.

Main Results:

• Identified a ~100-residue region at the chemoreceptor tip as the most rigid.
• Observed significant chemical shift changes between kinase-on and kinase-off signaling states in this rigid region.
• Demonstrated that dynamics differ across protein regions and between signaling states.

Conclusions:

• SSNMR can selectively detect and analyze key regions of large protein assemblies.
• Conformational changes occur at the chemoreceptor tip during signaling, not previously observed.
• SSNMR is a powerful tool for mechanistic studies of multi-protein complexes.