01Name both sides of the interaction

In receptor pharmacology, a ligand binds a receptor protein. Peptide ligands include endogenous signalling molecules and experimentally studied analogues. Many relevant receptors are located at the cell surface, where an extracellular interaction can influence events inside the cell.IUPHAR Pharmacology Education Project — Receptors (opens in a new tab)

Start a reading note with two fields: the precise peptide tested and the precise receptor studied. A family name alone may conceal several receptor subtypes. A familiar peptide name may conceal a fragment, terminal modification or experimental label. Neither abbreviation should replace the identity information in the methods.

For example, an experiment with a modified fragment at one named receptor does not directly establish how its unmodified parent behaves at every member of that receptor family. This is a scope check, even before considering the result.

02Recognition involves a molecular arrangement

A structural example comes from Zhang and colleagues' 2018 study of the human glucagon receptor with the peptide analogue NNC1702. The reported crystal structure showed contacts involving the peptide and receptor, together with changes in the receptor's extracellular stalk and first extracellular loop. This is evidence about that defined complex, rather than a universal diagram for all peptide receptors.Zhang and colleagues — Glucagon receptor bound to a glucagon analogue (opens in a new tab)

The practical lesson is that recognition concerns an arrangement of atoms in a particular molecular setting. A short shared sequence or a similar molecular mass is not enough to establish the same interaction. Conversely, a difference in sequence does not automatically exclude interaction; the relevant evidence must be examined.

03Separate three kinds of evidence

These are complementary questions. A paper can combine them, but a summary should not silently substitute one for another. A computationally proposed pose belongs in a further category: a model to examine against evidence. Calling a predicted interaction experimentally demonstrated removes an important distinction.

If only a downstream signal was measured, look for the experiments connecting that signal to the proposed receptor. Otherwise, the name attached to the pathway may be a hypothesis rather than a directly established binding partner.

04Binding does not specify the direction of action

Agonists can activate receptor-mediated signalling, whereas receptor antagonists can prevent an agonist's action without producing that same activation. Binding and activation therefore answer different questions. The functional label needs its own experimental basis.IUPHAR Pharmacology Education Project — Receptors (opens in a new tab)

Imagine two hypothetical ligands that both show measurable binding. One increases the selected signal when tested alone; the other prevents the first ligand's signal under a defined comparison. Describing both only as receptor-binding peptides would discard the most useful difference in those results.

The converse mistake is to assume that every observed increase means direct receptor agonism. Keep the molecular interaction claim and the response claim on separate lines until the study supplies the connection.

05Write a bounded interaction summary

• ✓Record the peptide form and receptor subtype or construct.
• ✓Identify whether the evidence is structural, binding, functional or computational.
• ✓Name the model, measured endpoint and relevant experimental conditions.
• ✓State what the evidence establishes without extending it to untested targets or products.

A clear sentence might say that a defined analogue interacted with a named receptor in a particular assay. Further sentences can then explain any measured response and its limits. That structure lets a reader see where the evidence ends without burying the central finding.