Spatial analysis of the ancient proteome of archeological teeth using mass spectrometry imaging

Abstract

RATIONALE Proteins extracted from archaeological bone and teeth are utilised for investigating the phylogeny of extinct and extant species, the biological sex and age of past individuals, as well as ancient health and physiology. However, variable preservation of proteins in archaeological materials represents a major challenge. METHODS In order to better understand the spatial distribution of ancient proteins preserved within teeth, we apply Matrix Assisted Laser Desorption/Ionisation Mass Spectrometry Imaging (MALDI-MSI) for the first time to bioarchaeological samples to visualise the intensity of proteins in archaeological teeth thin sections. We specifically explore the spatial distribution of four proteins (collagen type I, of which chains alpha -1 and 2, alpha-2-HS-glycoprotein, haemoglobin subunit alpha and myosin light polypeptide 6). RESULTS We successfully identify ancient proteins in archaeological teeth thin sections using mass spectrometry imaging. The data are available via ProteomeXchange with identifier PXD038114. However, we observe that peptides did not always follow our hypotheses for their spatial distribution, with distinct differences observed in the spatial distribution of several proteins, and occasionally between peptides of the same protein. CONCLUSIONS While it remains unclear what causes these differences in protein intensity distribution within teeth, as revealed by MALDI-MSI in this study, we demonstrate that MALDI-MSI can be successfully applied to mineralised bioarchaeological tissues to detect ancient peptides. In future applications, this technique could be particularly fruitful not just for understanding the preservation of proteins in a range of archaeological materials, but making informed decisions on sampling strategies and the targeting of key proteins of archaeological and biological interest.