Improved procedure for protein binder analysis in mural painting by LC-ESI/Q-q-TOF mass spectrometry: detection of different milk species by casein proteotypic peptides

Abstract

Diagnostic techniques applied to the field of cultural heritage represent a very important aspect of scientific investigation. Recently, proteomic approaches based on mass spectrometry coupled with traditional spectroscopic methods have been used for painting analysis, generating promising results for binder's protein identification. In the present work, an improved procedure based on LC-ESI/Q-q-TOF tandem mass spectrometry for the identification of protein binders has been developed for the molecular characterization of samples from an early-twentieth-century mural painting from the St. Dimitar Cathedral in Vidin, Bulgaria. The proteomic investigation has led to the identification of both egg white and egg yolk proteins, according to traditional old recipes for tempera paintings. In addition, beyond the egg components, the presence of caseins was also revealed, thus suggesting the use of milk as binding medium, fixative or stabilising agent. Furthermore, for the first time, the capability to discriminate the milk origin on the basis of alpha casein proteotypic peptides is reported, that are diagnostic for a given species, thus opening interesting perspectives in art and archaeological fields.

Multi-technique chemical characterisation of a 12–13th-century painted Crucifix

“…A comparison was also carried out with the peptides of various protein-based materials commonly found in paintings (i.e., egg yolk, egg white, animal glue, casein) as reported in literature [21,22,24,28,31,32] and with an internal database obtained from the analysis of standard samples. It is worth noting that proteinaceous binders are subjected to ageing processes accelerated by the occurrence of some catalytic pigments [27,44,45].…”

“…In particular, MALDI-MS offers a series of advantages such as direct analysis of complex mixtures with reduced sample pretreatment, short analysis times, relatively easy interpretation of results, and high sensitivity, fundamental in the study of paintings with very limited sample amounts. ESI-MS not only allows to identify proteins but also the protein species origin from few micrograms of artwork samples [31,33,35].…”

“…Py-GC/MS is particularly suitable for the analysis of synthetic polymers [12][13][14][15] or polymeric fractions of natural resins [16][17][18][19], whereas MALDI-TOF-MS has recently been shown to be efficient in fast and complete identification of historic paint binders. In fact, since a decade the use of new mass spectrometric techniques based on soft ionization, such as MALDI [20][21][22][23][24][25][26][27] or Electrospray Ionization (ESI) [25][26][27][28][29][30][31][32][33][34][35][36] for investigation of organic materials as present in polychrome artefacts or archaeological finds has significantly increased. In particular, MALDI-MS offers a series of advantages such as direct analysis of complex mixtures with reduced sample pretreatment, short analysis times, relatively easy interpretation of results, and high sensitivity, fundamental in the study of paintings with very limited sample amounts.…”

Proteomic identification of adhesive on a bone sculpture-inlaid wooden artifact from the Xiaohe Cemetery, Xinjiang, China

“…56 ± 10 ka) and Sibudu (ca. 70 ka) in the form of conifer resin and Acacia gum respectively (Charri e- Duhaut et al, 2013;Wadley et al, 2009), at the Western Asian site of Umm-el-Tlel (ca. 70 ka) in the form of bitumen (Bo€ eda et al, 2008), etc.…”

“…Immunoassay techniques, like ELISA, are specific and informative, but they are limited to targeted protein (Scott et al, 2009). More recently, proteomic approaches, based on high resolution mass spectrometry, have been utilized and rapidly developed for identification of archaeological protein binders due to their high sensitivity and accuracy which can determine the precise origin of the binder using very low sample amount (Chambery et al, 2009;Dallongeville et al, 2011bDallongeville et al, , 2013Fremout et al, 2010;Fremout et al, 2011;Leo et al, 2009).…”