α-helical conformations are an important part of protein function and contribute to assembly and folding. In order to understand the role of flexibility of these regions, we investigate the helical and electrostatic contributions to the persistence length (lp) of poly-L-lysine (PLL) independently by inducing a coil-helix transition by changing the pH, and probing the electrostatic effects by changing the solution ionic strength. Using static and dynamic light scattering, lp is determined from the salt- and pH-dependent Rg. In addition to Rg, hydrodynamic radius, (Rh), the shape factor (Rg/Rh), and second virial coefficient (A2) of the PLL for a range of salt and pH conditions are reported. In neutral pH, the polymer is a random coil, swollen by charge interactions. Increasing the ionic strength of the solvent reduces the polyelectrolyte lp and increases chain flexibility due to greater salt screening. Increasing the pH of the solvent leads to the partial and complete formation of helices and the dominance of the helical contribution to lp, which leads to an increase in rigidity, but not to the extent predicted by molecular dynamics simulations. By understanding the contributions to helical lp and their implications to polymer or protein flexibility, we can further understand the function of biomacromolecules.

Helical persistence length of Poly-L-Lysine

ACS Spring Meeting 2021

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