Single-molecule tracking of sub-millisecond domain motion in calmodulin

Area of Science:

• Biophysics
• Molecular Biology
• Biochemistry

Background:

• Calmodulin (CaM) is a crucial calcium-binding protein involved in numerous cellular processes.
• Understanding CaM's conformational dynamics is key to elucidating its regulatory mechanisms.
• Previous studies have investigated CaM dynamics, but high-resolution, time-resolved analyses are limited.

Discussion:

• Single-pair fluorescence resonance energy transfer (spFRET) was employed to monitor distance changes between CaM domains with sub-millisecond precision.
• The majority of observed CaM molecules remained within a stable conformational substate for up to 1 millisecond, suggesting slower conformational exchange.
• Apparent transitions between substates were detected in a subset of measurements, indicating dynamic flexibility.

Key Insights:

• CaM exhibits distinct conformational substates with significant stability on the sub-millisecond timescale.
• Subtle, yet measurable, domain fluctuations occur within dominant substates, influenced by environmental factors.
• Environmental conditions like pH and ionic strength modulate the dynamics of CaM's conformational substates.

Outlook:

• Further spFRET studies at even faster timescales could resolve the precise mechanisms of conformational interchange.
• Investigating CaM dynamics in complex cellular environments will provide deeper insights into its function.
• Correlating observed dynamics with CaM's interaction partners will illuminate its role in signal transduction pathways.