Interactions between biomolecules play a key role in every biological process. Mass photometry is ideally suited to quantify interactions at low concentrations with the major advantage that it can detect biological complexes present in solution. Molecular mass is a universal readout that informs on multiple properties, including the homogeneity, structural integrity and activity of biomolecules and biomolecular complexes. This means that mass photometry can be used not just for simple purity assays but also for activity and binding assessment, providing a unique level of data integrity and producing results that can be easily compared with those from other technologies.
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.
Figure 1 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.
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 2).
Measuring the affinity of protein-protein interactions on a single-molecule level by mass photometry
Wu et al., Analytical Biochemistry 2020, 592, 113575
In this work, the authors show how mass photometry can be used to study multivalent complexes and quantify the affinities of different binding sites in a single measurement.
Casposase structure and the mechanistic link between DNA transposition and spacer acquisition by CRISPR-Cas
Hickman et al., eLife 2020, 9:e50004
Mass photometry was used to characterise the oligomeric state of casposase alone and in a complex with different DNA constructs.