Receptor Binding Affinity
A measure of how strongly a molecule binds to its target receptor, typically expressed as a dissociation constant (Kd). Higher binding affinity means the molecule binds more tightly and remains attached longer. Modifications to a peptide's sequence can dramatically alter its binding affinity.
Technical Context
Binding affinity is quantified by the dissociation constant (Kd) — the ligand concentration at which 50% of receptors are occupied at equilibrium. Lower Kd = higher affinity. Affinity is determined by association rate (kon — how quickly the ligand binds) and dissociation rate (koff — how quickly it releases). For therapeutic peptides, high affinity generally correlates with potency but not always with efficacy. Very high affinity can sometimes lead to prolonged receptor activation causing desensitisation. Surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) are standard techniques for measuring peptide-receptor binding kinetics. Binding affinity data are a key component of preclinical pharmacological characterisation.