Short peptides are one of the most direct ways to ask whether a particular stretch of a protein is responsible for an interaction. Synthesize the region, measure whether it binds the partner, then change it residue by residue to find out which side chains matter. This hub collects what you need to plan that work: how to choose a binding method, how to design the peptide so the measurement means something, and how to read the numbers that come out.
A large share of protein-protein interactions are mediated by short linear motifs: a few residues in a disordered region or on an exposed loop that dock into a groove on the partner. Because the binding information is contained in a short stretch of sequence, a synthetic peptide can often reproduce the interaction outside the context of the full protein.
That makes peptides valuable in several ways. They let you test a hypothesis about which region binds without making mutant proteins. They give you a tractable starting point for an inhibitor. They can be labeled, immobilized or arrayed far more easily than a full-length protein. And they can be made as a series — alanine mutants, truncations, phospho and non-phospho pairs — so that a structure-activity relationship emerges from one coherent set of molecules.
This is worth being clear about before designing an experiment, because it determines how the result should be reported.
| A peptide experiment can tell you | It cannot tell you on its own |
|---|---|
| Whether a given sequence region is sufficient to bind the partner | Whether that region is the only contributor in the intact protein |
| Which side chains within the motif are required | Whether distant residues contribute through the folded structure |
| An affinity for the isolated motif | The affinity of the full-length interaction, which is often much tighter |
| Whether a modification such as phosphorylation changes binding | Whether that modification occurs at a meaningful level in cells |
Isolated peptides very often bind more weakly than the parent protein. The peptide pays an entropic cost that the folded protein does not, because the protein already holds the motif in a favorable conformation, and it loses any contacts made by residues outside the motif. A peptide KD in the micromolar range for an interaction that is nanomolar between full-length proteins is a common and unremarkable result, not evidence that the motif is wrong.
The single most common mistake
Running the whole study in one assay format with no orthogonal check. Every method has characteristic artifacts, and a peptide that looks like a binder in one format alone is not yet a binder. Confirming a hit in a second, mechanistically different method is the cheapest insurance in this field.
Paste a peptide or protein sequence to review length, charge, hydrophobicity and other properties before you order.
Research use only. LifeTein peptides and proteins are supplied for laboratory research use. They are not for human or veterinary use, and not for diagnostic or therapeutic use. See our research use policy.
If you are planning a binding study and would like a second opinion on peptide design, controls or assay format before you order, email sales@lifetein.com with the sequence and the question you are trying to answer, or use our quotation form. Design review is part of the service, not an extra.