Investigation of proteins in samples of a mid-18th century colonial mural painting by MALDI-TOF/MS and LC-ESI/MS (Orbitrap)

Abstract

In this paper, we report the study of proteinaceous binders in samples from a South American Colonial 18th century painting using two complementary mass spectrometry techniques. Before restoration, seven micro-samples were extracted from representative colors of one of the mural paintings located inside the church of Our Lady of Copacabana de Andamarca built in 1723 in Bolivia. Previous analysis by gas chromatography (GC) of the amino acid derivatives of the extracted protein fraction of three of the samples, suggested the presence of animal glue and egg. In this work, we introduce a methodology that combines a protein extraction procedure with a typical treatment for analysis of proteins as tryptic peptides by mass spectrometry. For this study, we applied in the first stage, MALDI-TOF/MS and then, LC-ESI/MS (Orbitrap), an ultrahigh resolution mass spectrometry, to achieve more reliability in the identification of the protein binders. By LC-ESI/MS (Orbitrap), we detected several peptides from egg white proteins, particularly ovalbumin, ovotransferrin and lysozyme, and egg yolk proteins, vitellogenin-2 and apolipoprotein B, with high confidence peptides each. In all the samples, the presence of collagen from animal provenance was established by MALDI-TOF/MS and LC-ESI/MS (Orbitrap). To our knowledge, this is the first time that protein binders in Andean paintings are identified without ambiguity by MALDI-TOF/MS and LC-ESI/MS (Orbitrap) mass spectrometry using a proteomic approach.