Internal friction in an intrinsically disordered protein-Comparing Rouse-like models with experiments

Area of Science:

• Protein dynamics
• Polymer physics
• Biophysics

Background:

• Internal friction is a key factor in protein dynamics, even in unfolded states.
• The molecular origins of internal friction remain poorly understood.
• Existing polymer theories struggle to fully explain experimental observations.

Purpose of the Study:

• To compare four polymer theories of internal friction with experimental data.
• To investigate the dynamics of the intrinsically disordered protein ACTR.
• To elucidate the relationship between chain dimensions and internal friction.

Main Methods:

• Utilized nanosecond fluorescence correlation spectroscopy (nc-FCS).
• Employed single-molecule Förster resonance energy transfer (smFRET).
• Studied ACTR dynamics across varying solvent viscosities and compaction levels.

Main Results:

• All tested theories successfully modeled the viscosity-dependence of ACTR's chain relaxation time.
• No current theory could explain the observed slowdown in dynamics upon ACTR chain collapse.
• A mechanistic link between protein compaction and internal friction is still lacking.

Conclusions:

• Current polymer theories for internal friction are incomplete.
• Internal friction in disordered proteins is likely a composite phenomenon.
• Further research is needed to understand the multifaceted nature of internal friction in protein dynamics.