Direct Observation of Single-Protein Transition State Passage by Nanopore Ionic Current Jumps

Prabhat Tripathi, Arash Firouzbakht, Martin Gruebele, Meni Wanunu

Research output: Contribution to journalArticlepeer-review


Conformational transitions of proteins are governed by chemical kinetics, often toggled by passage through an activated state separating two conformational ensembles. The passage time of a protein through the activated state can be too fast to be detected by single-molecule experiments without the aid of viscogenic agents. Here, we use high-bandwidth nanopore measurements to resolve microsecond-duration transitions that occur between conformational states of individual protein molecules partly blocking pore current. We measure the transition state passage time between folded and unfolded states of a two-state λ6-85mutant and between metastable intermediates and the unfolded state of the multistate folder cytochrome c. Consistent with the principle of microscopic reversibility, the transition state passage time is the same for the forward and backward reactions. A passage time distribution whose tail is broader than a single exponential observed in cytochrome c suggests a multidimensional energy landscape for this protein.

Original languageEnglish (US)
Pages (from-to)5918-5924
Number of pages7
JournalJournal of Physical Chemistry Letters
Issue number25
StatePublished - Jun 30 2022
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry


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