Semiflexible Ring Polymers on Active Motor Beds: Nonequilibrium Dynamics and Conformations

A semiflexible ring polymer on a motor-protein bed exhibits activity- and processivity-dependent rotational and conformational dynamics that are not captured by linear-chain behavior. Using coarse-grained Langevin simulations with bending elasticity, excluded-volume interactions, and stochastic motor attachment, stepping, and detachment, we vary activity (Peclet number), motor processivity, and chain stiffness to map the nonequilibrium response. The mean-squared displacement shows crossover dynamics, with semiflexible rings displaying subdiffusive-to-diffusive behavior at low activity and an intermediate ballistic regime at higher activity, while increasing flexibility shifts the short-time response toward a Rouse-like limit. Diameter autocorrelations exhibit damped oscillations associated with coherent rotation; the rotational frequency increases with activity and processivity, whereas the decorrelation time is non-monotonic at high processivity. Fourier mode analysis identifies competition between the radius (k=0) and elliptic (k=2) modes as the origin of the non-monotonic asphericity.