Unique Electrical Signature of Phosphate for Specific Single-Molecule Detection of Peptide Phosphorylation.

Single-molecule measurements of biomaterials bring novel insights into cellular events. For almost all of these events, post-translational modifications (PTMs), which alter the properties of proteins through their chemical modifications, constitute essential regulatory mechanisms. However, suitable single-molecule methodology to study PTMs is very limited. Here we show single-molecule detection of peptide phosphorylation, an archetypal PTM, based on electrical measurements. We found that the phosphate group stably bridges a nanogap between metal electrodes and exhibited high electrical conductance, which enables specific single-molecule detection of peptide phosphorylation. The present methodology paves the way to single-molecule studies of PTMs, such as single-molecule kinetics for enzymatic modification of proteins as shown here.

Measurement of Electron Transfer within a Single Supramolecular Assembly Containing a Biological Molecule.

We report on a method to measure the electron transport of a single molecular assembly by scanning tunneling microscopy (STM). The STM molecular tip together with a chemically modified substrate was utilized to form an assembly with a single target molecule. This method was successfully applied to a heme peptide to reveal the transport property of a single peptide-containing assembly. The present work opens a way to create functional single molecular devices using biomolecules.