Molecular Competition between Large and Small Polyethylene-Glycols (PEGs) Partitioning into OMPC Porin Channels

Abstract

Molecular crowding by polyethylene glycols (PEGs) has been employed in a wide range of inquiries into molecular structure and dynamics. Investigating the partitioning of crowded polymers into biological nanopores reveals properties also seen in, e.g., DNA ejection and compaction into viral capsids, as well as in facilitated molecule transport. Capitalizing on our previous work on the partitioning of binary PEG mixtures into the benchmark Alpha-Hemolysin nanopore, we have now studied partitioning of mono- and polydisperse polymer solutions into comparably sized, yet differently structured, diffusion channels. We find that in the presence of large non-partitioning PEG 3400, the small, otherwise equipartitioning PEG 200 partitions disproportionately. Specifically, with 15% PEG 3400, an added 15% PEG 200 reduces channel conductance by 65% (compared with channel conductance in polymer-free solutions), while 15% PEG 200 alone reduces channel conductance by only 45%. We employed open-channel noise analysis to investigate channel diffusion properties of individual polymers, and to compare them with their properties in bulk water solution. In this way we demonstrate and quantify crowding-assisted transport through nanopores in mixed-polymer systems.