The folding of various biopolymers, ranging from proteins to chromosomes, into specific conformations is vital for cellular function. Longstanding research has unveiled basic principles of polymer folding from the perspective of equilibrium thermodynamics. In the cell, however, thermodynamic constraints such as the fluctuation-dissipation relation can cease to hold, due to the presence of active processes which consume energy and provide local excitations. Based on this idea, we used analytical theory to investigate how a polymer responds to excitations that are heterogeneous in magnitude or are correlated along the polymer sequence. We have found that, on the level of the steady-state distribution of conformations, athermal excitations elicit effective long-ranged attraction or repulsion, which can be mapped to an effective equilibrium model where the polymer is constrained by additional springs. Thus, one cannot distinguish the folding patterns of an active polymer from those of a passive polymer through structural data alone. These results point towards a need for dynamic measurements to distinguish active from passive effects. However, the dynamical properties of such inhomogeneous active polymers have remained largely unexplored, and it is not clear what to expect from experiments. To address this question with theory, we study the fluctuation properties of heterogeneous active polymers, from single locus and pair mean squared displacements to pairwise velocity correlations as a function of lag time and measurement time window.
Hosts: Michael Abbott, Isabella Graf, and Mason Rouches
