Semiflexible ring polymers on active motor beds: Nonequilibrium dynamics and conformations

Area of Science:

• Soft matter physics
• Polymer dynamics
• Biophysics

Background:

• Linear polymer behavior on motor proteins is well-studied.
• Ring polymers exhibit distinct conformational and dynamic properties due to their topology.
• Understanding polymer behavior on active substrates is crucial for cellular processes.

Purpose of the Study:

• To investigate the rotational and conformational dynamics of semiflexible ring polymers on a motor-protein bed.
• To map the nonequilibrium response by varying activity, motor processivity, and chain stiffness.
• To compare ring polymer dynamics with established linear-chain behaviors.

Main Methods:

• Coarse-grained Langevin simulations were employed.
• Key factors included bending elasticity, excluded-volume interactions, and stochastic motor dynamics (attachment, stepping, detachment).
• Parameters varied were activity (Péclet number), motor processivity, and chain stiffness.

Main Results:

• Mean-squared displacement showed crossover dynamics: subdiffusive-to-diffusive at low activity, with a ballistic regime at higher activity.
• Increased flexibility shifted short-time dynamics towards a Rouse-like limit.
• Diameter autocorrelations revealed damped oscillations indicating coherent rotation, with frequency increasing with activity and processivity.

Conclusions:

• Semiflexible ring polymers exhibit unique activity- and processivity-dependent dynamics not seen in linear chains.
• The interplay between different Fourier modes (k=0 and k=2) explains nonmonotonic asphericity changes.
• This study provides insights into the complex behavior of polymers in active environments.