The effect of crowder charge in a model polymer–colloid system for macromolecular crowding: Polymer structure and dynamics

Abstract

We have examined the effect of crowder particle charge on macromolecular structure, studied via small-angle neutron scattering, and translational dynamics, studied via pulsed-field gradient NMR, in addition to bulk viscosity measurements, in a polymer macromolecule (polyethylene glycol)-nanoparticle crowder (polysucrose, Ficoll70) model system, in the case where polymer size and crowder size are comparable. While there are modest effects of crowder charge on polymer dynamics at relatively low packing fractions, there is only a tiny effect at the high packing fractions that represent the limit of molecular crowding. We find, via different measures of macromolecular mobility, that the mobility of the flexible polymer in the crowding limit is 10-100 times larger than that of the compact, spherical crowder in spite of their similar size, implying that the flexible polymer chain is able to squeeze through crowder interstices.

Dynamics and cluster formation in charged and uncharged Ficoll70 solutions

“…Figure 7 shows plots of the diffusion coefficient of Ficoll70 for different packing fraction Φ F , in the presence of small amounts of a polymeric macromolecule, polyethyelene glycol (PEG), in the concentration range 0.003 − 0.03g/cm 3 ). PEG is the macromolecule used in the companion work 26 . A weak effect on Ficoll70 dynamics has been observed at the lowest Φ F and highest c p : this is reasonable because we have already inferred that the PEG and Ficoll70 do not associate with each other.…”

Confined crowded polymers near attractive surfaces

“…We vary φ c between 0.035 to 0.435 in steps of 0.05, by changing the number of crowder particles between 950 and 11750. The range of crowder densities considered in this work is similar to the range used in previous work 4,47,48 . We also perform simulations of a polymer in a good solvent placed in a periodic box, thus mimicking the unconfined case, so as to compare our results with results for the confined case.…”

Diffusion NMR and Rheology of a Model Polymer in Bacterial Cell Lysate Crowders

“…Macromolecular crowding typically results in a reduction in the diffusivity of a test probe macromolecule in the intracellular milieu, compared to its diffusion in dilute solution. ,− Palit and co-workers (2017) explored the effect of artificial charged and uncharged Ficoll crowders on polyethylene glycol (PEG) as the test probe polymer, showing that the crowder charge has a small effect on the diffusivity of the uncharged PEG, reflecting the possible importance of “soft” interactions. , Although artificial and biological crowders have been examined for their effects on the diffusion of macromolecules such as proteins, there is still much to investigate about the role of biological crowders. A fundamental question is how a realistic crowding environment–characterized by macromolecules with and without charge as well as naturally occurring polydispersity in size–affects test molecule diffusivity. ,, …”

“…PEG is also used to precipitate proteins and has been found to phase separate in solution . According to diffusion NMR experiments performed by Palit et al, the PEG overlap concentration c * is of order ∼5 mg/ml; other measurements put c * ∼30 mg/ml. The overlap concentration in a polymer indicates (roughly) the point of crossover between the dilute and semidilute regime.…”

“…17 What causes these differences is unknown, 2 but could be related to differences in diffusivity in crowded environments between compact and chain-like probe molecules. 18 Macromolecular crowding typically results in a reduction in the diffusivity of a test probe macromolecule in the intracellular milieu, compared to its diffusion in dilute solution. and uncharged Ficoll crowders on polyethylene glycol (PEG) as the test probe polymer, showing that the crowder charge has a small effect on the diffusivity of the uncharged PEG, reflecting the possible importance of "soft" interactions.…”