Supermetallization of peptides and proteins during electrospray ionization

Abstract

The formation of metal-peptide complexes during electrospray ionization (ESI) is a widely known phenomenon and is often considered to be undesirable. Such effect considerably limits the use of ESI mass spectrometry for the investigation of biologically relevant metal-peptide compounds that are present in the solution and play critical roles in many bioprocesses such as progression of neurodegenerative diseases. In the article, it is demonstrated that under specific conditions such as high temperature of the desolvating capillary, an interesting effect, which can be called as 'supermetallization', occurs. Using a model peptide Αβ amyloid domain 1-16, it was observed that an increase in the temperature of the desolvating capillary results in multiple substitutions of hydrogen atoms by Zn atoms in this peptide. At high temperatures (T ~ 400 °C), up to 11 zinc atoms can be covalently bound to (1-16) Αβ. It was observed that supermetallization of (1-16) Αβ depends on the solvent composition and pH. Supermetallization was also demonstrated for proteins, such as ubiquitin and cytochrome C. That proves that the supermetallization is a general phenomenon for peptides and proteins. For the structural investigation of supermetallized complexes, electron-capture dissociation (ECD) fragmentation was applied. The effect of hydrogen rearranging during ECD was observed. In addition, quantum chemical calculations were used to estimate the possible structures of different supermetallized complexes. These results allow a more deep understanding of the limitations of the use of ESI mass spectrometry for the investigation of biologically relevant metal-peptide complexes. Copyright © 2015 John Wiley & Sons, Ltd.

Crosstalk of the structural and zinc buffering properties of mammalian metallothionein-2

“…This fact has been underlined recently by two recent reports proving that investigations of Zn(II)-peptide/ protein equilibria by ESI in the gas phase are not quantitative due to zinc deposition or protein supermetalation during analysis. 64,65 Nevertheless, such a dynamic picture shows that two possible Zn(II) binding pathways may occur ''clustered'' via cluster formation and ''beaded'' via formation of individual coordination sites prior to coalescence into a cluster, as was postulated in a recent study. 14 On the other hand, our results strongly support the model in which initial metal ion binding takes place only in the a-domain.…”

The Functions of Metamorphic Metallothioneins in Zinc and Copper Metabolism

“…Our results of Zn 2+ binding to T performed in the presence of Zn 2+ donors with various affinities (unpublished data) demonstrate that metal binding analysis performed by ESI-MS does not assess completely the equilibria present in solutions. Two recent papers published in mass spectrometry journals prove that investigations of Zn 2+ -equilibria by electrospray ionization in the gas phase are not quantitative due to zinc deposition or protein supermetallation during ESI-MS analysis [104,105]. …”

Thermal dissociation of ions limits the degree of the gas‐phase H/D exchange at the atmospheric pressure

“…Recently, several groups have been focused on the use of the in‐ionization source H/D exchange for the enumeration of the labile hydrogens in the complex organic mixtures, peptides, proteins, oligosaccharides, and oligonucleotides . It was shown that high temperature of desolvating capillary can lead to such exotic effects as deuterium exchange at non‐labile sites, gas‐phase 16 O/ 18 O exchange, and formation of complexes of proteins with unusually high number of metals . Previously, investigating the H/D exchange of the proteins in the standard Thermo LTQ interface, we have encountered the impossibility to achieve the good degree of the reaction even at the highest temperature the capillary could be heated to (450 °C).…”