Mass Photometry to facilitate Biomedical research at York

We propose to purchase a mass photometer system which is a new technology for determining masses of proteins and other large biological molecules in solution. Many proteins form oligomers containing several subunits, or interact in complexes bound to other proteins. Understanding these complex formations is vital in understanding the mechanisms of disease and other biological processes and for example enable new drug targets. Finding out the masses of these particles gives vital information about their composition and stability and requires a method that does not disrupt the complexes nor require excessive amounts of sample. The mass photometer "weighs" particles by capturing the disturbance they cause in reflected light as they adhere to a small glass slide. By observing mixtures of proteins we can see if they bind together - for example an antigen with an antibody, or a hormone to its receptor, and also whether these are one-to-one or several-to-one interactions, which is often difficult to determine with other methods. The information will be valuable for detecting and measuring interactions between proteins, working out the sizes of the complexes they form and enabling structural studies of their structures. The instrument is relatively simple to operate and will be used by doctoral students and other researchers, enabled by its location in an efficiently run core facility environment, with training, method development and data analysis supported by expert core-funded facility staff.

The mass photometer uses a technique also known as ISCAMS (Interferometric scattering mass spectrometry) although it has more in common with refractive index detection or light scattering than with traditional MS. An interferogram created at the surface of a glass slide is perturbed by the adsorption of protein or other particles with a different refractive index. The disturbance is proportional to mass and detected as single binding events, so observation over a period generates a histogram or distribution plot of the different mass particles present. Calibration is achieved using standard protein samples of known MW. The useful mass range is 50 kDa to 3 MDa and the concentration required is in the nM range with volumes of about 10 microlitres. Such picomole quantities enable studies on samples hitherto too scarce and difficult to prepare for more traditional techniques. The measurements are compatible with most common buffer ingredients enabling direct determination of the formation and stoichiometry of protein complexes or oligomers under mild and relatively physiological conditions. The technique has a number of advantages over existing methods - vs native PAGE, less effect of charge and buffer; vs MALLS, much lower sample size; vs mass spectrometry, no solvents or evaporation into vacuum. In addition measurement takes only a few minutes per sample to perform. Rich information about the sample and easy low cost data collection opens the way to rapid screening of samples and binding conditions not only as an end in itself but also as an underpinning to more time consuming and expensive techniques such as SPR and CryoEM. This will enable rapid analysis of many functional and structural protein components of important disease related processes. The system is suitable for operation by users and located in a core facility where training, method development and data analysis will be supported by expert core-funded staff.