Figure 1: Protein-protein interactions
Antigen-antibody interactions are a prime example of molecular systems that can be studied using mass photometry, which can be applied to determine binding affinities for mono- and multivalent interactions.
illustrates how mass photometry can be used to quantify molecular interactions. By measuring the mass of the antibody trastuzumab and its target antigen, Her2, individually and in mixtures, the interactions between individual antibody molecules and target antigens could be quantified.
Figure 2: DNA-protein interactions
Mass photometry can be used to characterise DNA-protein complexes, which are crucial in gene expression, replication and DNA repair.
In this example, mass photometry not only allows detection of DNA binding but also provides information on how the oligomeric state of the protein changes upon DNA binding.
Figure 3: Protein oligomerization
Many proteins adopt a particular oligomeric form under certain conditions. In Figure 1, mass photometry characterises four different proteins: protein A, beta-amylase, urease and thyroglobulin. Through this characterisation, these proteins showcase a range of behaviours – from purely monomeric (as in Protein A) to a dynamic equilibrium between multiple states.
Complex formation
Ribosomes are macromolecular assemblies of protein and RNA, and are central sites for protein synthesis. Bacterial ribosomes (in this example from E. coli) are >2 MDa in size. Magnesium ions play a subtle yet important role in the assembly of intact (70S) complexes. In the absence of magnesium, E. coli ribosomes rapidly disassemble into their 30S and 50S subunits. Mass photometry allows us to monitor these processes (Figure).
