Sample characterisation
Sample purity and stability are crucial elements of successful biochemical and structural studies. In the context of pharmaceutical production, the purity of proteins is of particular importance, especially with the increasing prevalence of protein-based products such as biologics.
Mass photometry provides a rapid assessment of sample heterogeneity at a single molecule level, using minimal volumes of sample and in a matter of minutes. Mass distributions obtained with mass photometry provide direct information about existing species in your sample, and any variations due to changing conditions can be used for sample optimisation.
Antibodies
Mass photometry is a new way to assess the quality of biotherapeutics such as antibodies. In the example illustrated in Figure 1, we present the mass distribution of NISTmAb (a humanized IgG1κ monoclonal antibody) and its degradation after a period of long term storage at +4 °C, as observed using the DiscoverMP software.
Apoferritin vs holoferritin
Apoferritin (ApoF) is a globular protein complex consisting of 24 protein subunits forming a nanocage. In the presence of iron, ApoF interacts with multiple ions, forming a complex called holoferritin, or simply ferritin. Each molecule of ferritin can store thousands of iron (Fe3+) ions, which causes a shift in mass distribution. The difference in mass between apo- and holoferritin and the broad iron-core mass distribution of holoferritin, can be seen in Figure 2.
DNA
Mass photometry is universal in its applicability, since all molecules scatter light, irrespective of whether they are based on amino-acids, lipids, nucleic-acids or carbohydrates.
Figure 3 illustrates a standard DNA ladder (Invitrogen) that was measured with mass photometry and used as a calibration to determine the mass of 2,686 bp (~1.8 MDa) DNA plasmid (pUC18).
Related publications
Quantifying the heterogeneity of macromolecular machines by mass photometry
Sonn-Segev et al., biorxiv 2019
A recent study in which mass photometry was used in workflows involving multi-step purification processes and chemical crosslinking. Results on various systems, including respiratory complex I, anaphase-promoting complex, proteasomes and cohesin, illustrate the unique advantages of mass photometry for rapid sample characterization, prioritization and optimization.
Mass Photometry of Membrane Proteins
Olerinyova et al., biorxiv 2020
This publication shows examples of mass photometry applied to samples containing either detergents, amphipols or nanodiscs, paving the way for the characterisation of samples of membrane proteins.
