Resolving heterogeneous macromolecular assemblies by Orbitrap-based single-particle charge detection mass spectrometry

We demonstrate single-particle charge detection mass spectrometry on an Orbitrap for the analysis of megadalton biomolecular assemblies. We establish that the signal amplitudes of individual ions scale linearly with their charge, which can be used to resolve mixed ion populations, determine charge states and thus also determine the masses of individual ions. This enables the ultrasensitive analysis of heterogeneous protein assemblies including immunoglobulin oligomers, ribosomes, proteinaceous nanocontainers and genome-packed adeno-associated viruses. An Orbitrap-based method for single-particle charge detection mass spectrometry enables facile, ultrasensitive analysis of protein assemblies.