Abstract
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Charge
deconvolution infers the mass from mass over charge (m/z) measurements in electrospray ionization
mass spectra. When applied over a wide input m/z or broad target mass range, charge-deconvolution algorithms
can produce artifacts, such as false masses at one-half or one-third
of the correct mass. Indeed, a maximum entropy term in the objective
function of MaxEnt, the most commonly used charge deconvolution algorithm,
favors a deconvolved spectrum with many peaks over one with fewer
peaks. Here we describe a new “parsimonious” charge
deconvolution algorithm that produces fewer artifacts. The algorithm
is especially well-suited to high-resolution native mass spectrometry
of intact glycoproteins and protein complexes. Deconvolution of native
mass spectra poses special challenges due to salt and small molecule
adducts, multimers, wide mass ranges, and fewer and lower charge states.
We demonstrate the performance of the new deconvolution algorithm
on a range of samples. On the heavily glycosylated plasma properdin
glycoprotein, the new algorithm could deconvolve monomer and dimer
simultaneously and, when focused on the m/z range of the monomer, gave accurate and interpretable
masses for glycoforms that had previously been analyzed manually using m/z peaks rather than deconvolved masses.
On therapeutic antibodies, the new algorithm facilitated the analysis
of extensions, truncations, and Fab glycosylation. The algorithm facilitates
the use of native mass spectrometry for the qualitative and quantitative
analysis of protein and protein assemblies.
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