Conjugation of Amphiphilic Proteins to Hydrophobic Ligands in Organic Solvent

Protein-ligand conjugations are usually carried out in aqueous media in order to mimic the environment within which the conjugates will be used. In this work, we focus on the conjugation of amphiphilic variants of elastin-like polypeptide (ELP), short elastin (sEL), to poorly water-soluble compounds like OPPVs (p-phenylene vinylene oligomers), triarylamines, and polypyridine-metal complexes. These conjugations are problematic when carried out in aqueous phase because hydrophobic ligands tend to avoid exposure to water, which in turn causes the ligand to self-aggregate and/or interact non-covalently with hydrophobic regions of the amphiphile. Ultimately, this behavior leads to low conjugation efficiency and contamination with strong non-covalent “conjugates”. After exploring the solubility of sEL in various organic solvents, we have established an efficient conjugation methodology for obtaining covalent conjugates virtually free of contaminating non-covalent complexes. When conjugating carboxylated ligands...