Europium probe binding to serum albumin and α1-AGP, key importance of configuration, charge and size complementarity

Combined luminescence studies and stochastic molecular dynamics simulations have revealed for the first time how cooperative hydrophobic binding and reversible metal ion coordination to protein glutamate residues occurs. A combined experimental and theoretical approach has been used to explain the very different free energies of binding observed between three structurally analogous chiral europium(iii) complexes and common variants of serum albumin. In particular, reversible binding of a carboxylate from a glutamate residue was observed; this residue is found in human serum albumin but not the other variants. The binding free energy is exquisitely sensitive to the europium probe structure and charge, and favours complexation of a right handed stereoisomer in the chiral binding pocket. Each process has been visualised by short movies, revealing probe conformational exchange dynamics and the pathway to the protein binding site, on a sub-microsecond timescale.