Observation of Intact and Proteolytically Cleaved Amyloid-Beta (1-40)-Oleuropein Noncovalent Complex at Neutral pH by Mass Spectrometry.

Ioana Cezara Caba,Bogdan Ionel Tamba,Raluca Ştefănescu

doi:10.3390/molecules26113261

Ioana Cezara Caba, Bogdan Ionel Tamba + Show 1 more

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https://doi.org/10.3390/molecules26113261

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Abstract

Mass spectrometry analyses carried out on mass spectrometers equipped with soft ionization sources demonstrated their utility in the assessment of the formation of noncovalent complexes and the localization of the binding sites. Direct analyses by mass spectrometry of the noncovalent complex formed in acidic and mildly acidic environments by amyloid beta (1–40) peptide and oleuropein have been previously described, and, in several studies, the absorption, metabolism, excretion, and the implications in the prevention and therapy of Alzheimer’s disease of oleuropein have been investigated. Our paper presents modifications of the method previously employed for noncovalent complex observation, namely, the amyloid beta (1–40) pretreatment, followed by an increase in the pH and replacement of the chemical environment from ammonium acetate to ammonium bicarbonate. The formation of noncovalent complexes with one or two molecules of oleuropein was detected in all chemical solutions used, and the amyloid beta (17–28) binding site was identified via proteolytic experiments using trypsin prior to and after noncovalent complex formation. Our results highlight the importance of further studies on the effect of oleuropein against amyloid beta aggregation.

Highlights

The study of noncovalent complexes, and the identification of molecules’ binding regions, is essential for biomedical studies, as it allows for the investigation of the interaction of different molecules in living organisms and the effects exerted by foreign molecules to which living organisms are exposed
Both electrospray ionization (ESI) and matrix assisted laser desorption and ionization (MALDI) were proven to be effective ionization methods for the analysis of noncovalent complexes and of compounds belonging to different classes of molecules; studies aimed at analyzing noncovalent complexes at neutral pH using MALDI are less frequent [1,2]
By increasing the pH to 7.35, the noncovalent complex was identified in ammonium acetate and ammonium bicarbonate

Summary

Introduction

The study of noncovalent complexes, and the identification of molecules’ binding regions, is essential for biomedical studies, as it allows for the investigation of the interaction of different molecules in living organisms and the effects exerted by foreign molecules to which living organisms are exposed. Direct analysis by mass spectrometry of complexes formed in a solution is possible by using a chemical medium similar to those found in the human physiology and ensuring the mass spectrometric compatibility of the chemical solutions containing the molecules whose interactions are studied Both electrospray ionization (ESI) and matrix assisted laser desorption and ionization (MALDI) were proven to be effective ionization methods for the analysis of noncovalent complexes and of compounds belonging to different classes of molecules; studies aimed at analyzing noncovalent complexes at neutral pH using MALDI are less frequent [1,2]. The latter approach allows the selection of a chemical medium which contains inorganic ions and biomolecules resembling the body chemical environment in which the interaction takes place

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