Characterization of membrane metal threads by proteomics and analysis of a 14th c. thread from an Italian textile

Abstract Beginning in the 13th century, membrane metal threads – made out of animal skins (leather, parchment, and vellum) or membranous material (e.g., stomach, intestine) coated with metal – were the most popular variety of decorative metal threads used in European textiles. This work provides the proteomics groundwork for the identification of the species and the type of membrane used in the manufacture of a 14th century membrane gilded thread. A protocol for small sample extraction and nanoLC-Orbitrap MS/MS analysis was first tested on standards of pig peritoneum and cow intestine metal-coated with or without the presence of an egg adhesive. The proteomes of each membrane were characterized and compared by qualitative and quantitative bioinformatics; in addition to the predominant collagen proteins in each membrane type, minor tissue-specific proteins (e.g., smooth muscle proteins from intestine standards) were detected. Species-specific collagen peptides (i.e., from collagen I and collagen III) were confidently identified to determine the species of origin, regardless of the application of metal and egg-based adhesives. Likewise, the thin layer of egg adhesive was successfully characterized with the detection of egg white (ovalbumin, ovotransferrin, lysozyme) and egg yolk (vitellogenin I, II, III) proteins. When applied to the thread from a 14th century Italian textile, this comprehensive methodology resulted in the identification of seven collagen I and III peptides specific to cow, as well as other proteins suggesting that the ancient thread was made with intestine or stomach membrane without the use of an egg-based adhesive.