Semisynthesis of Aminomethyl-Insulin: An Atom-Economic Strategy to Increase the Affinity and Selectivity of a Protein...

Advancements in the molecular recognition of insulin by nonantibody-based means would facilitate the development of methodology for the continuous detection of insulin for the management of diabetes mellitus. Herein, we report a novel insulin derivative that binds to the synthetic receptor cucurbit[7]uril (Q7) at a single site and with high nanomolar affinity. The insulin derivative was prepared by a four-step protein semisynthetic method to present a 4-aminomethyl group on the side chain of the Phe^B1 position. The resulting aminomethyl insulin binds to Q7 with an equilibrium dissociation constant value of 99 nM in neutral phosphate buffer, as determined by isothermal titration calorimetry. This 6.8-fold enhancement in affinity versus native insulin was gained by an atom-economical modification (-CH₂NH₂). To the best of our knowledge, this is the highest reported binding affinity for an insulin derivative by a synthetic receptor. This strategy for engineering protein affinity tags induces minimal change to the protein structure while increasing affinity and selectivity for a synthetic receptor.