Introduction to Protein - Protein Interactions

Central to advancements in the understanding of biochemical processes, is the study of protein - protein interactions.

Proteins are at the heart of all biological systems within a cell, while many proteins perform their duties individually, the majority of proteins function within complexes. Complete knowledge of all direct and indirect interactions of proteins within a cell is the next important milestone for the comprehensive mapping of cellular mechanisms and functions.


  • Protein - protein interactions encompasses:
  • Receptor - ligand interaction studies
  • Kinetic studies of enzymes.
  • Binding site determination in small molecules.
  • Specificity determination of proteins.
  • Cell signalling.
  • Drug Screening.

Some of the ways researchers currently study protein - protein interactions include:


Crosslinking reagents are used to capture protein-protein complexes by forming a covalent bond between them as they interact. The rapid reactivity of the crosslinkers means even transient or weakly interacting molecules can be captured for characterisation.

Co-Immunoprecipitation (Co-IP).

Co-IP targets known proteins that are part of a larger complex of proteins. By targeting the known protein with its specific antibody, it is possible to pull the entire protein complex for analysis by standard Western Blot methods.

Affinity Chromatography.

Affinity chromatography separates proteins on the basis of a reversible interaction between a protein (or protein complex) and a specific ligand coupled to a chromatography matrix. The technique offers high selectivity, high resolution, and usually high capacity for the protein of interest.

Surface Plasmon Resonance (SPR).

SPR is an optical technique for detecting the interaction between two different proteins, where one is mobile (in an analyte) and the other is fixed to an ultra-thin gold film. SPR biosensors respond with high sensitivities and in real-time to the binding of proteins via a change in optical response plotted in a sensorgram (see figure). SPR sensors can detect sub-femtomolar levels of proteins and other small molecules in the few kiloDalton size range.

The Affinity system uses similar detection principles as SPR. By using a nanostructured sensing surface and exploiting localised surface plasmon resonances (LSPR), Causeway Sensors has been able to reduce the size and cost of the biosensor.


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