Jump transition observed in translocation time for ideal poly-X proteinogenic chains as a result of competing folding and anchoraging contributions

摘要

In this work we analyze the translocation of homopolymer chains poly-X, where X represents any of the20 naturally occurring amino acid residues, in terms of size N and single-helical propensity ω. We providean analytical framework to calculate both the free energy F of translocation and the translocation time τ as afunction of chain size N, energies U and ε of the unfolded and folded states, respectively. Our results show thatfree energy F has a characteristic bell-shaped barrier as function of the percentage of monomers translocated.Inclusion of single-helical propensity ω associated to monomer X and chain’s native energy ε in the translocationmodel increases the energy barrier ΔF up to one order of magnitude as compared with the well-known Gaussianchain model. Computation of the mean first-passage time as function of chain size N shows that the translocationtime τ exhibits a significant jump of several orders of magnitude at a critical chain size N. This jump markedlyslows down translocation of chains larger than N. Existence of the transition jump of τ has been observedexperimentally at least in poly(ethylene oxide) chains [R. P. Choudhury, P. Galvosas, and M. Schoenhoff, J. Phys.Chem. B 112, 13245 (2008)]. Our results suggest the transition jump of τ as a function of N may be a very wellspread feature throughout translocation of poly-X chains.