  Polymer translocation in crowded environments is a ubiquitous phenomenon in
biological systems. We studied polymer translocation through a pore in free,
one-sided (asymmetric), and two-sided (symmetric) crowded environments.
Extensive Langevin dynamics simulation is employed to model the dynamics of the
flexible polymer and crowding particles. We studied how crowding size and
packing fraction play a crucial role in the translocation process. After
determining the standard scaling properties of the translocation probability,
time, and MSD, we observed that the translocation rate and bead velocities are
location-dependent as we move along the polymer backbone, even in a crowd-free
environment. Counter-intuitively, translocation rate and bead velocities showed
the opposite behavior; for example, middle monomers near the pore exhibit
maximum bead velocity and minimum translocation rate. Free energy calculation
for asymmetrically placed polymer indicates there exists a critical number of
segments that make the polymer to prefer the receiver side for translocation.
For one-sided crowding, we have identified a critical crowding size above which
there exists a non-zero probability to translocate into the crowding side
instead of the free side. Moreover, we have observed that shifting the polymer
towards the crowded side compensates for one-sided crowding, yielding an equal
probability akin to a crowder-free system. Under two-sided crowding, the
mechanism of how a slight variation in crowder size and packing fraction can
force a polymer to switch its translocation direction is proposed, which has
not been explored before. Using this control we achieved an equal translocation
probability like a crowd-free scenario. These conspicuous yet counter-intuitive
phenomena are rationalized by simple theoretical arguments based on osmotic
pressure and radial entropic forces.
