  In biology, there are several processes in which unfolded protein chains are
transported along narrow-tube channels. Normally, without such a severe
configurational constraint, unfolded polypeptides would not bind to each other.
However, when chain entropy is much reduced in the narrow channel, we find that
polypeptide chains have a propensity to bind, even if there is no great
potential energy gain in doing so. We find the average length of binding m*
(the number of monomers at the chain ends that form bonds) and the critical
tube diameter at which such constrained binding occurs. We carry out Brownian
dynamics simulations of tightly confined chains, demonstrating their binding
over the characteristic length m*, changing in tubes of different diameter.
