Investigation of proteins in samples of a mid-18th century colonial mural painting by MALDI-TOF and nano-LC-ESI-hybrid-Q-orbitrap mass spectrometry

LEVY, IVANA KARINA; NEME TAUIL, RICARDO MARTÍN; MORENO DE COLONNA, SILVIA; SIRACUSANO, GABRIELA; MAIER, MARTA

Bilbao

Congreso; TECHNART 2017 Non-destructive and Microanalytical Techniques in Art and Cultural Heritage; 2017

Universidad del País Vasco

With the aim of investigating the presence of proteinaceous materials in a wall painting from the church of Our Lady of Copacabana de Andamarca (1723) in Bolivia, seven micro-samples have been extracted before the restoration. Historically, artists have used different proteinaceous binders as egg, casein, and animal glues, depending on the painting technique and their availability. Identification of proteinaceous binders plays an important role in conservation and offers insights into the manufacturing technique of a work of art.In this investigation, we report for the first time the application of proteomic tools to the study of colonial samples. The analysis of proteinaceous binders was performed on references, model samples and micro-samples from a wall painting. In the first stage of our study, we applied MALDI-TOF mass spectrometry and then, we used nano-LC-ESI-hybrid-Q-orbitrap to achieve more reliability in the identification of the protein binders.By MALDI, we found weak signals presumably of egg peptides in several of the micro- samples. By nano-LC-ESI-hybrid-Q-orbitrap, one sample yielded several peptides from seven egg white different proteins, particularly ovoalbumin, ovotransferrin, lysozyme, and two egg yolk proteins, vitellogenin-2 and apolipoprotein B, were detected in another sample with one high confidence peptide each. These results confirm our previous GC-MS results indicating that egg tempera was used as the painting technique [1]. In all the samples, the presence of collagen from animal glue was established by MALDI-TOF and nano-LC-ESI-hybrid-Q-orbitrap. This finding supported our previous assumption that animal glue was applied as a primer onto the ground layer. In order to identify the origin of the collagen isoforms, a search against a Uniprot database containing collagen proteins from all the species was performed. The results suggest that this glue was prepared from a mixture of several sources.In conclusion, both mass spectrometry techniques are efficient tools for identifying proteinaceous binders in old tempera paintings. The advantage of nano-LC-ESI-hybrid-Q-Orbitrap over MALDI-TOF lies in the highest accuracy to identify proteins. However, MALDI allowed a quicker screening and faster comparison between samples and references.