Date : Thursday, December 17, 2020, 03:30 PM (UTC+1), auditorium of ENSTBB, Bordeaux.
Title : "New developments in high-resolution mass spectrometry for proteomic analysis applied to cultural heritage: study of intact proteins, their cross-linkages and interactions in artworks and museum objects".
Summary : Proteins in cultural heritage objects constitute a critical source of information. Their detection and characterisation can provide an accurate comprehension of the artist’s technique and formulations. A more in-depth insight of the state of conservation and history of the artwork can also be achieved through investigation at the molecular level of the degradation mechanisms induced by natural ageing, environmental factors or either by inappropriate conservation/restoration treatments. Firstly, the PhD was dedicated to the development of proteomic bottom-up and top-down strategies using mass spectrometry for the study of proteins at trace levels from historical and artistic objects. The potentialities of a combination of these two complementary approaches were highlighted in the study of Gainsborough’s drawings, where the presence of milk-based fixatives was revealed with samples collected with minimally invasive techniques. Information achieved with the peptidic analysis, such as the specific breed origin of the detected proteins and their modifications, were enriched through top-down analysis with the detection of highly modified proteoforms characterised by multiple cleavage patterns. Secondly, the PhD study aimed to achieve a better insight into the proteins’ structural and conformational alterations in an artwork. A strategy based on the elaboration of data from the bottom-up analysis was optimised to investigate the protein networks formations through the localisation and characterisation of cross-linked peptidic pairs. The methodology was initially tested on mock-ups of paintings (formulated with lysozyme mixed with lead white pigment) which were treated with oxidising agents and naturally aged. The detection of different reticulated products led to defining various molecular patterns characteristic of oxidative-based cross-links in the lysozyme protein which subsequently were detected in more complex samples from historical tempera paintings. The cross-linking examination, combined with an unbiased modification search, also was effective for a more exhaustive understanding of the conservation history of a Coptic manuscript subjected to ancient invasive restoration treatment. The detection of a great extent of lysine methylations and especially the characteristic fragmentation markers of formaldehyde-based cross-links provided the first analytical evidence of a potential parchment consolidation treatment based on gelatin-formol used by the Vatican library during restoration. The developed approach also offered a more accurate protein identification detecting peptides that passed unnoticed in the classical strategy because they were chemically modified or structurally unreachable. Finally, the action of some of the most common inorganic pigments on proteins molecular and structural changes was also investigated. Particularly, the role of these inorganic compounds in proteins conformational changes was investigated for the first time through Hydrogen/Deuterium exchange (HDX) studies via mass spectrometry (intact protein approach). The decrease of deuterium exchange observed for certain mixtures suggested the interposition of the pigment in the protein solvent accessibility, or/and the modification of the molecular conformation.
Members of the jury :
Dr Arslanoglu Julie, Department of Scientific Research, The Metropolitan Museum of Art, USA.
Professor Birolo Leila, University of Naples Federico II, Italy.
Professor associate Bonaduce Ilaria, University of Pisa, Italy.
Professor Chapoulie Rémy, University of Bordeaux Montaigne, France.
Professor Collins Matthew, University of Copenhagen, Denmark.
Dr Dufourc Erick, Centre National de la Recherche Scientifique, Bordeaux, France.
Dr Menu Michel, Centre de Recherche et de Restauration des Musées de France, France.
Professor Tokarski Caroline, University of Bordeaux, France.
Information of the PhD : The doctoral project of Galluzzi Francesca has been supported by the Marie Skłodowska‐Curie European Training Network (ETN) “TEMPERA” for paleoproteomic analysis of cultural heritage (http://www.tempera-etn.eu). The project focused on mass spectrometry-based ancient protein residues analysis for biomolecular diagnostics and conservation of cultural heritage material.