Extending the capabilities of mass spectrometry

Mass spectrometry can provide information about the composition of large biomolecular machines, but only if the instrument can handle high mass-to-charge ratios (m/z) with good resolution. That becomes even harder with complexes that include both proteins and nucleic acids because the nucleic acids don’t acquire enough charge to bring the complexes within the mass range of most instruments. A team led by Albert J. R. Heck of Utrecht University has now modified an Orbitrap mass spectrometer so that it has an ultrahigh mass range, more than twice that of the commercially available Orbitrap extended mass range instrument (Nat. Methods 2017, DOI: 10.1038/nmeth.4147). The researchers achieved this improvement with modifications that increased the transmission and resolution of ions with greater than 20,000 m/z. To demonstrate the instrument’s performance, the researchers analyzed intact bacterial ribosomes and their subunits. The improvements enabled the researchers to resolve relatively small mass differences associated with heterogeneity in the subunits and with the binding of a small ribosomal-associated protein. The researchers also showed that the instrument could analyze a 9-megadalton virus. They propose that such high mass capabilities could make mass spectrometry useful as a quality-control tool for large biological complexes prior to analysis by electron microscopy or crystallography.