Gas-phase electrophoretic mobility
molecular analysis (GEMMA) separates
nanometer-sized, single-charged particles according to their electrophoretic
mobility (EM) diameter after transition to the gas-phase via a nano
electrospray process. Electrospraying as a soft desorption/ionization
technique preserves noncovalent biospecific interactions. GEMMA is
therefore well suited for the analysis of intact viruses and subviral
particles targeting questions related to particle size, bioaffinity,
and purity of preparations. By correlating the EM diameter to the
molecular mass (Mr) of standards, the Mr of analytes can be determined. Here, we demonstrate
(i) the use of GEMMA in purity assessment of a preparation of a common
cold virus (human rhinovirus serotype 2, HRV-A2) and (ii) the analysis
of subviral HRV-A2 particles derived from such a preparation. (iii)
Likewise, native mass spectrometry was employed to obtain spectra
of intact HRV-A2 virions and empty viral capsids (B-particles). Charge
state resolution for the latter allowed its Mr determination. (iv) Cumulatively, the data measured and published
earlier were used to establish a correlation between the Mr and EM diameter for a range of globular proteins and
the intact virions. Although a good correlation resulted from this
analysis, we noticed a discrepancy especially for the empty and subviral
particles. This demonstrates the influence of genome encapsulation
(preventing analytes from shrinking upon transition into the gas-phase)
on the measured analyte EM diameter. To conclude, GEMMA is useful
for the determination of the Mr of intact
viruses but needs to be employed with caution when subviral particles
or even empty viral capsids are targeted. The latter could be analyzed
by native MS.