Electrolyte chemistry plays an important role in the transport properties of analytes through nanopores. Here, we report the translocation properties of the protein human serum transferrin (hSTf) in asymmetric LiCl salt concentrations with either positive (
- NSF-PAR ID:
- 10276368
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 11
- Issue:
- 39
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 24398 to 24409
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Ctrans /Ccis < 1) or negative chemical gradients (Ctrans /Ccis > 1). Thecis side concentration was fixed at 4 M for positive chemical gradients and at 0.5 M LiCl for negative chemical gradients, while thetrans side concentration varied between 0.5 to 4 M which resulted in six different configurations, respectively, for both positive and negative gradient types. For positive chemical gradient conditions, translocations were observed in all six configurations for at least one voltage polarity whereas with negative gradient conditions, dead concentrations where no events at either polarity were observed. The flux of Li+and Cl−ions and their resultant cation or anion enrichment zones, as well as the interplay of electrophoretic and electroosmotic transport directions, would determine whether hSTf can traverse across the pore. -
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null (Ed.)Many small proteins move across cellular compartments through narrow pores. In order to thread a protein through a constriction, free energy must be overcome to either deform or completely unfold the protein. In principle, the diameter of the pore, along with the effective driving force for unfolding the protein, as well as its barrier to translocation, should be critical factors that govern whether the process proceeds via squeezing, unfolding/threading, or both. To probe this for a well-established protein system, we studied the electric-field–driven translocation behavior of cytochrome c (cyt c ) through ultrathin silicon nitride (SiN x ) solid-state nanopores of diameters ranging from 1.5 to 5.5 nm. For a 2.5-nm-diameter pore, we find that, in a threshold electric-field regime of ∼30 to 100 MV/m, cyt c is able to squeeze through the pore. As electric fields inside the pore are increased, the unfolded state of cyt c is thermodynamically stabilized, facilitating its translocation. In contrast, for 1.5- and 2.0-nm-diameter pores, translocation occurs only by threading of the fully unfolded protein after it transitions through a higher energy unfolding intermediate state at the mouth of the pore. The relative energies between the metastable, intermediate, and unfolded protein states are extracted using a simple thermodynamic model that is dictated by the relatively slow (∼ms) protein translocation times for passing through the nanopore. These experiments map the various modes of protein translocation through a constriction, which opens avenues for exploring protein folding structures, internal contacts, and electric-field–induced deformability.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1RA03903B
