Separation of mass spectra of hydrogen-deuterium exchanged ions obtained by electrospray of solutions of biopolymers with unknown primary structure.

The work is dedicated to further development of our described method for analyzing mass spectra of biomolecules acquired as a result of hydrogen-deuterium exchange reactions (HDXs). The modified method consists of separating HDX distributions via their approximations by a minimum number of components corresponding to independent H/D substitutions and independent charge carrier retentions in different spatial isoforms or conformations of biomolecules with unknown primary structures. In this case, neither the natural isotopic distribution nor the exact number of active sites involved in HDXs and H or D attachments can be determined in advance.

Two-dimensional decomposition of H-D exchange mass spectra of multicharged ions of biopolymers and their separation into components with independent H-D substitutions.

The work is aimed at developing a numerical method for analysing mass spectra of deutero-substituted multicharged ions of biopolymers to determine contributions of components presumably corresponding to different biomolecule conformations. The two-dimensional decomposition of the H-D exchange mass spectra of two, three and four charged apamin ions with their separation suggests that the reaction of apamin ions with ND molecules in the gas phase reveals hypothetically three different structural modifications of apamin ions. Usually for H-D exchange mass spectra, the presence of many resolvable protein structures was determined from measured distributions of peak intensities of ions with the same charge state.

Two possible improvements for mass spectrometry analysis of intact biomolecules.

The goals of our study were to investigate abilities of two approaches to eliminate possible errors in electrospray mass spectrometry measurements of biomolecules. Passing of a relatively dense supersonic gas jet through ionization region followed by its hitting the spray of the analyzed solution in low vacuum may be effective to keep an initial biomolecule structure in solution. Provided that retention of charge carriers for some sites in the biomolecule cannot be changed noticeably in electrospray ion source, decomposition and separation of charge-state distributions of electrosprayed ions may give additional information about native structure of biomolecules in solution.

[Probabilistic calculations of biomolecule charge states that generate mass spectra of multiply charged ions].

In this work, information relating to charge states of biomolecule ions in solution obtained using the electrospray ionization mass spectrometry of different biopolymers is analyzed. The data analyses have mainly been carried out by solving an inverse problem of calculating the probabilities of retention of protons and other charge carriers by ionogenic groups of biomolecules with known primary structures. The approach is a new one and has no known to us analogues.

Decomposition of charge-state distributions for better understanding of electrospray mass spectra of bioorganic compounds. Part 2: application of the method.

The results of the analysis of electrospray mass spectra of b-endorphin and chicken egg lysozyme in different conditions of data acquisition using the method described in Part 1 of the work are reported. At least partial unfolding during the process of ion formation in the electrospray ion source of an initially native biomolecule of lyzozyme in solution should supposedly explain the received set of probabilities of proton retention by basic and acidic residues of this molecule for all considered conditions of data acquisition.