Question: what evidence can distinguish peptide binding from productive receptor activation?

A peptide can show clear receptor binding without necessarily producing the claimed biological response. Affinity alone may not establish whether it stabilises an active receptor state, behaves as a partial agonist, recruits a different signalling complex, or simply occupies the site without productive coupling.

What would a convincing mechanism-of-action package look like for a peptide receptor ligand? I am interested in how researchers would combine binding kinetics, receptor mutagenesis, structural or biophysical evidence, proximal signalling measurements and pathway-level functional assays. In particular, which observations are genuinely informative about efficacy rather than just correlation?

It would also be useful to discuss how to interpret differences between recombinant systems and endogenous cells, where receptor density, accessory proteins and feedback could alter the apparent pharmacology. Are there accepted experimental designs for separating affinity, residence time, receptor conformational change and downstream efficacy, or does the appropriate evidence depend too heavily on the receptor class?