Charge state deconvolution

Zhang, Z. and Marshall, A. G. A universal algorithm for fast and automated charge state deconvolution of electrospray mass-to-charge ratio spectra. /. Am. Soc. Mass Spectrom., 9, 225, 1998. 

Wilkes, J.G., Buzatu, D.A., Dare, D.J., Dragan, Y.P., ChiareUi, M.P., Holland, R.D., Beaudoin, M., Heinze, T.M., Nayak, R., Shvartsburg, A.A., Improved cell t5fping by charge-state deconvolution of MALDI mass spectra. Rapid Commun. Mass Spectrom. 2006, 20, 1595. 

Fig. 11.19. Partial ESI mass spectrum of BSA and molecular weights after charge deconvolution (inset). Charge states are assigned to both series of peaks. Reproduced from Ref. [24] by permission. John Wiley Sons, 2000.

Fig. 9.3 Flowchart illustrating how data is automatically handled and processed to yield the chemical structure of a hit. The LC/MS systems have been integrated with software to automatically deconvolute each protein charge state distribution and determine potential protein conjugation and obtain the structure of a hit by database searching.

Figure 7.5 Deconvoluted, zero charge state mass spectrum demonstrating a hit from a DCL-targeting metallo-[3-lactamase (Bell). The dominant peak corresponds to anrora A kinase linked to extender 23, which is in turn linked to fragment 24 to give 25 (dynamic hit ). Reprinted from Reference 27, with permission from Elsevier, Copyright (2008).

If the protein molecular weight is unknown, then the charge states are also not known. The process of determining the molecular weight for an unknown protein from such a mass spectrum is known as deconvolution and is based on simple algebra. If MW is the... 

Data for comparison to the model were obtained via the electrospray ionization mass spectrum of a Starburst PAM AM dendrimer (core = NH3) generation = 4 between m/z 600 and 1600. The ESI mass spectrum consisted predominantly of multiple charged ions at +7, +8, +9, +10, and +11 charge states. The deconvoluted mass spectrum between 9600 and 10747 daltons suggest the presence of at least 16 components in the sample. The last significant peak at 10632 daltons corresponds with the theoretical mass 10632.96, magic number which is within one mass unit for the ideal generation = 4 structure (see Fig. 33). 

This distribution of charges, especially when there may be more than one molecular species, can represent a very confusing picture. This situation may be further compounded by the presence of additional ion series that can occur when protonation competes with cations such as sodium and potassium. However, it is possible to deconvolute the multiple charge states and to calculate the mass of the molecule in question, by application of simple algebra. 

Figure 5.9 (a) Raw mass spectrum from scans 2(X)0-2025 of the eighth fraction. Stars indicate the charge state distribution of 16 293 Da. Circles indicate the charge distribution of 11 824 Da. (b) The deconvoluted mass spectrum of (a) obtained by MaxEntl. Reproduced from F. Zhou and M. Johnston, Electrophoresis, 28, 1383-1388 (2005), with permission from Wiley-VCH... 

Accurate calibration of the mass scale is especially important when determining the masses of biopolymers because errors are magnifled during deconvolution, e.g., a 0.1 Da error for a 10 charge state ion becomes a 1 Da error when the observed mk value is multiplied by 10 to obtain the mass of the analyte. With good mass calibration, the experimental error in the molecular mass for a small protein, such as myoglobin, is 1 Da. 

Molecules of >1 kDa form multiply charged ions appearing as an envelope (skewed to lower m/z) that must be deconvoluted (transformed) to obtain the molecular mass of the neutral, zero charge state... 

A. Dobo and I. A. Kaltashov, Detection of multiple protein conformational ensembles in solution via deconvolution of charge-state distributions in ESI MS, Anal. Chem. 73, 4763-4773 (2001). 

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