Cees Dekker's protein sequencing paper

Cees Dekker’s group recently published progress toward nanopore protein sequencing. The work addresses one of the fundamental issues in nanopore protein sequencing, controlling the translocation speed.

Without this, peptides translocate too quickly for individual amino acids to be detected (for more context on this see the Dreampore post). As there are no established techniques for controlling peptide translocation the Dekker approach links a peptide to a DNA molecule. This allows motion control techniques established for DNA sequencing to be applied to protein sequencing.

Specifically, they us a DNA helicase to pull DNA (and the linked peptide) through an MspA nanopore:

In the paper they only use negatively charged peptides. This means the construct as a whole has a negative charge, and is pulled through the pore under the bias voltage. The Helicase works in the opposite direction, pulling the conjugate back through the pore.