Charge state distribution

The apphcation of mass spectrometry to the stndy of a protein s higher-order structures requires a protocol in which differences in the miz ratio associated with each distinct conformation of the protein conld be monitored. One common mass spectrometry methods for conformational analysis is charge-state distribution (CSD) [24]. This method can be implemented only with the ESI mode of analysis. CSD provides a qualitative, low-resolution picture of the conformational state of a protein. Positive-ion ESI generates a distribntion of mnltiply charged 

In the seminal work, it was demonstrated that changes in the ESI-CSD profile of cytochrome c can be correlated with fluctuations in its conformation induced by the pH of the solution [24]. Disruption in the native state of a protein with a change in the solution temperature, addition of denaturing agents, and cleavage 

The CSD method is straightforward and simple to implement, but the results should be interpreted with caution because the reproducibility of the ESI ion profile might fluctuate due to changes in various experimental variables, such as pH, temperature, solution composition, and the ESI ion-source settings (e.g., gas flows and voltages). 

Solution Because there are eight basic residues (four K, three R, and one H) and one terminal amino group, a maximum of 94- charge states might be 

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Note that for the determination of molecular weight, the charge-state distribution is not of great importance as it does not affect the m/z value of the ion involved and thus the calculated molecular weight. If the conformational state of the biopolymer is of interest, however, the distribution of charged states is a fundamental consideration and any parameter likely to change this distribution must be carefully controlled. 

Grandori, R. Origin of the conformation dependence of protein charge-state distributions in electrospray ionization mass spectrometry. I. Mass Spectrom. 2003,38, 11-15. 

H. J. Hofmann, G. Bonani, M. Suter and W. Wolfli, Charge state distributions and isotopic fractionation, Nucl. Instrum. Methods B 29, 100 104 (1987). 

A. T. Iavarone, J. C. Jurchen, and E. R. Williams. Effects of Solvent on the Maximum Charge State and Charge State Distribution of Protein Ions Produced by Electrospray Ionization. J. Am. Soc. Mass Spectrom., 11(2000) 976-985. 

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.

Monitoring conformational changes by charge state distribution (CSD)... 

Denatured proteins will have a broader charge state distribution. 

The dependence of the protein conformation on the charge state distribution of its ions produced by ESI can be applied to study protein conformation. This also allows the denaturation process to be followed over this time and sometimes possible intermediates... 

In addition, inner-shell ionization contributes to the intensity of the z line. The removal of an inner-shell electron leads directly to the ls2s excited level of the He-like system. The contribution of this process is proportional to the concentration of the Li-like ions and should be taken into account at low electron temperatures or if the charge state distribution differs from ionization equilibrium. 

Within the last 25 years of X-ray spectroscopy on fusion devices, the theory of He-like ions has been developed to an impressive precision. The spectra can be modeled with deviations not more than 10% on all lines. For the modeling, only parameters with physical meaning and no additional approximation factors are required. Even the small effects due to recombination of H-like atoms, which contribute only a few percent to the line intensity, can be used to explain consistently the recombination processes and hence the charge state distribution in a hot plasma. The measurements on fusion devices such as tokamaks or stellarators allow the comparison to the standard diagnostics for the same parameters. As these diagnostics are based on different physical processes, they provide sensitive tests for the atomic physics used for the synthetic spectra. They also allow distinguishing between different theoretical approaches to predict the spectra of other elements within the iso-electronic series. The modeling of the X-ray spectra of astronomical objects or solar flares, which are now frequently explored by X-ray satellite missions, is now more reliable. In these experiments, the statistical quality of the spectra is limited due to the finite observation time or the lifetime of... 

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