Controlled Photoiniferter RAFT-Based Development of Linear Polymers Induced by the Presence of a Peptide to Produce Synthetic Antibody Substitutes Applicable to Immunofluorescence Imaging Techniques

The fabrication of synthetic receptors that mimic the behavior of antibodies is attracting widespread attention, given their affinity and improved stability over those of their natural counterparts. In accordance with the mutually induced-fit principle, where flexible chains mutually induce the organization of each other, herein, we describe the fabrication linear copolymers as complementary chains to peptide epitopes. The production of these linear polymers is performed via controlled solid-phase polymerization by reversible addition-fragmentation chain transfer using a photo<i>iniferter</i> (PI-RAFT), pouring the monomer mixture onto glass beads having a peptide immobilized on their surface. This peptide influences the monomer arrangement in linear polymers generated at the surface, functioning as a template. PI-RAFT polymerization has enabled the production of polymers with half, equal to, or twice the size of the target peptide, the latter showing maximum affinity (<i>K</i>_D<i>:</i> 9.09 ± 0.27 nM). The present study focuses on the cannabinoid CB₁ receptor as a target protein and its linear C-terminal intracellular sequence as an epitope targeted by the polymers described herein. Accordingly, a synthetic 12 amino acid peptide matching that sequence was used as a template, achieving polymers with outstanding recognition capacity toward the target protein, also being evidenced here by their applicability to dual-labeling immunofluorescence assays toward CB₁ receptor-expressing cells.