Mass Spectrometry of an Intact Virus

Abstract

The mass analysis of virus particles is performed by using electrospray-ionization time-of-flight mass spectrometry with charge detection through the simultaneous measurement of the number of charges on each viral ion and the ion , s mass-to-charge ratio (m/z). The m/z ratio is obtaind through time-of flight measurements. Find out more on the following pages. The development of electrospray ionization (ESI) for biomolecular analysis marks one of the historically significant events in mass spectrometry (MS). [1] As a consequence largely of electrospray, the utility of mass spectrometry has been extended far beyond routine determinations of molecular weight to applications in such diverse fields as chemistry, immunology, and structural biology. [2] For example, ESI allows for the analysis of noncovalent interactions [3, 4] such as those that form the basis of supramolecular chemistry, [5] protein folding, [3, 6] and viral protein ± protein interactions. [7, 8] In fact, experiments performed on whole viruses [8] demon-strate that viruses can be observed with mass spectrometry and that noncovalent supramolecular structures can success-fully withstand the rigors of vaporization, ionization, and the vacuum of a mass spectrometer. In the initial experiments [8] viral ions to be analyzed by ESI were nondestructively introduced into the vacuum of a mass spectrometer and electrostatically focused onto a collector plate within the instrument. Interestingly, the virus particle ions were found to retain both their native structure and infectivity; however, mass measurements could not be obtained with the available mass spectrometers. We have circumvented the problems associated with detecting large ions by using charge-detection mass spectrometry to make a simultaneous measurement of charge (z) and mass-to-charge (m/z) ratio for individual particles. In previous experiments it was found that tobacco mosaic virus (TMV) could be passed through a quadrupole mass analyzer in radio frequency-only mode and weakly detected with an electron multiplier. [8] Yet in those studies we were unable to perform mass analysis on intact virus ions because their mass-to-charge (m/z) values were too large to yield peaks in our quadrupole mass spectrometer which had a m/z range of 2300. Furthermore, even if our instrument had had sufficient mass range, the limited resolution as well as formation of adducts during electrospray ionization would have made traditional determination of the mass by assign-ment of the charge state of adjacent peaks extremely difficult or impossible.