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 biologic drugs, such as therapeutic antibodies.
Mass photometry rapidly assesses 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 knowledge of variations due to changing conditions can inform sample optimisation.
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 shifts its mass distribution. The difference between the tightly peaked apoferritin mass distribution and the broad mass distribution of ferritin with an iron core, can be seen in Figure 2.
Mass photometry is universally applicable, since all molecules scatter light, irrespective of whether they are composed of amino acids, lipids, nucleic acids or carbohydrates.
Figure 3 illustrates the mass distribution of a standard DNA ladder that was measured with mass photometry and used as a calibrant to determine the mass of a 2,686 bp (~1.8 MDa) DNA plasmid (pUC18).
Related application notes
Quantifying the heterogeneity of macromolecular machines by mass photometry
Sonn-Segev et al., Nature Communications 2020
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 characterisation, prioritisation and optimisation.
Mass Photometry of Membrane Proteins
Olerinyova et al., Chem 2021
This publication shows examples of mass photometry being applied to samples containing either detergents, amphipols or nanodiscs, paving the way for the characterisation of samples of membrane proteins.