Identification of protein binders in eighteenth century Andean paintings

NEME TAUIL, RICARDO; FERNANDEZ GERMAN; VALACCO, MARIA PIA; MAIER, MARTA; MORENO, SILVIA

Congreso; LIX Annual Meeting SAIB 2023; 2023

In this work we present the study of protein binders in samples of 18th century paintings, two from murals of churches located in the northern region of Chile (Levy et al, 2021) and one located in the current Bolivian territory (Levy et al, 2018), using two complementary mass spectrometry techniques. We introduce a Methods that combines a protein extraction procedure with a typical treatment for analysis as tryptic peptides by mass spectrometry. We applied MALDI-TOF/MS and subsequently LC-ESI/MS (Orbitrap) to achieve higher reliability in identification.In the first two murals the protein fraction of the samples was extracted with ammonia following a previously optimized Methods and analyzed by LC-MSMS. We identified collagen as well as egg white and yolk proteins according to a tempera painting technique. In addition, we detected for the first time the presence of muscle proteins in two of the microsamples. Collagen and muscle proteins could be attributed to bovine (Bos taurus) and llama (Vicugna pacos), a domesticated camelid used as a source of food and for goods transport in the Andes since pre-Hispanic times.In the third church seven microsamples of representative colors were extracted from one of the mural paintings. Previous analysis by gas chromatography (GC) of the amino acid derivatives of the protein fraction extracted from three of the samples suggested the presence of animal glue and egg. We detected several peptides from egg white proteins, in particular ovalbumin, ovotransferrin and lysozyme, and from egg yolk proteins, vitellogenin-2 and apolipoprotein B, with peptides of high confidence. The presence of collagen was determined in all samples.These findings provide new aspects on the knowledge of the composition of ancient animal glues and painting practices in the Andean region, with reliable information useful for restoration and conservation work. This is also the first time that protein binders have been unambiguously identified in Andean paintings by mass spectrometry