Selective Protein‐Surface Sensing Using Ruthenium(II) Tris(bipyridine) Complexes

Abstract

Inhibition of protein–protein interactions (PPIs) with designed molecules represents a key challenge in modern bio-organic chemistry.[1–3] In contrast to competitive enzyme inhibition,[4] in which small molecules are optimised to masquerade as a substrate (or transition-state analogue) and fit a well defined concave pocket or cleft, competitive inhibition of PPIs requires a molecule that must make discontinuous, noncovalent contacts over a much larger (>800 A2), surface-lacking, defined shape. Whilst high-throughput screening has identified inhibitors of some PPIs,[5,6]—these are generally regarded as ‘low-hanging fruit’[2]—there remains a need to develop our basic understanding of how to design molecules that possess the features needed for protein-surface recognition. Building on fundamental studies of short peptide recognition,[7–9] a number of approaches in which a scaffold is used to project groups capable of making multivalent hydrophobic,[10] ion-pairing[11–29] and metal–ligand interactions[30–33] with proteins have been described. In the current manuscript we illustrate that functionalised RuII tris-bipyridine complexes can be used as selective and low nanomolar sensors for cytochrome c (cyt c).[34] Receptors for cyt c have been described[11–13,16–18,20–26] in addition to inhibitors of its PPIs.[35–37] The current system, however, offers significant advantages for fundamental studies of protein-surface recognition. Binding to metalloproteins and nonmetalloproteins can be detected by using simple fluorescence quenching or anisotropy changes, respectively, whilst structure–affinity studies and screening against a panel of proteins point to specific interactions with the target. Importantly, the highest affinity receptor binds cyt c with 1:1 stoichiometry and an affinity of 2 nm.