Identification of the protein components of historical artefacts can provide important information about cultural practices, the existence and use of natural resources in a particular culture or geographical area, or potentially rediscover “novel” bio-compounds for manufacturing purposes. In a recent study by Pires and others, LC-MS/MS was used to study the protein components of the binding material in a paint sample that remained on a gold artefact painted over 1000 years ago, presumably by members of the Sicán culture of Peru. The researchers found that after excluding skin and saliva proteins that were likely the result of contamination during excavation of the item, that the dominant proteins in the paint sample were from human blood and bird eggs. The identity and source of these proteins may be key to the paint’s longevity, but also provided support for archaeological theories regarding the cultural significance of the item located in an elite tomb of a member of the Sicán culture.
How was PEAKS used?
Data analysis was performed using the database search workflow in PEAKS Studio 8.5v. Sequential searches with general databases (all Uniprot proteins), followed by historically and geographically relevant sample- or species- specific databases allowed the researchers to narrow down the source of the proteins to human and bird, likely a species of duck known to be raised and eaten by the Sicán culture.
Pires E, Carvalho LDC, Shimada I, McCullagh J. Human Blood and Bird Egg Proteins Identified in Red Paint Covering a 1000-Year-Old Gold Mask from Peru. J Proteome Res. 2021 Nov 5;20(11):5212-5217. doi:10.1021/acs.jproteome.1c00472. Epub 2021 Sep 28. PMID: 34582218.
Abstract
We analyzed a red paint sample from the surface of a gold mask excavated from a Middle Sicán elite tomb in Peru. The mask covered the face of the principal male and dates from ca. 1000 AD, a period when many painted precious metal objects were produced. The paint’s inorganic pigment was identified more than 30 years ago as cinnabar (a mercuric sulfide scarlet-red to brown-red mineral), but the identity of the effective organic binder remained a mystery. Fourier transform infrared (FTIR) analysis of the sample indicated a proteinaceous composition, and no lipids were recovered from an N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) derivatized extract of the sample analyzed by gas chromatography-mass spectrometry (GC-MS). Proteomics analysis by nanoLC-MS/MS identified unique peptides in the sample, which were matched to human blood and bird egg proteins via Uniprot database searches. These included immunoglobulin heavy chain, immunoglobulin G, serum albumin, and ovomucoid. Cinnabar-based paints were typically used in the context of social elites and ritually important items. The presence of human blood would support previous ideas that red cinnabar paint may represent “life force” intended to support “rebirth”. As the red paint sample came from the first scientifically excavated Sicán gold mask, the results suggest a method to authenticate similar unprovenanced masks now in private and museum collections. Proteomics data set identifier https://doi.org/10.5287/bodleian:1ajYbBgQP.