Preserve and protect: non-destructive screening for protein preservation in ancient skeletal material

Abstract

Protein preserved in ancient bone provides us with phylogenetic, chronological and behavioural insights that are crucial for understanding human prehistory. Yet given the destructive nature of these biomolecular analyses, it is beneficial to determine the likely protein preservation of ancient skeletal material prior to analysis, to limit destructive sampling where chances of successfully retrieving data are low. A range of methods are used to assess organic preservation in skeletal material prior to sampling for aDNA, proteomic, isotopic or radiocarbon dating [e.g. 1-2], but these methods generally require destructive sampling of small amounts of material (several milligrams) and exportation to a lab. Near infrared (NIR) spectroscopy has been shown to be a useful method for assessing the bulk collagen content of bone before extraction for isotopic or radiocarbon analysis [3]. NIR pre-screening is fast, the instruments are transportable and, crucially, scanning is completely non-destructive. The approach has been successfully applied as a screening method for Pleistocene assemblages prior to dating [4]. As palaeoproteomic analysis using tandem mass spectrometry can be successfully carried out at much lower levels of protein preservation than radicoarbon dating, we tested the potential of NIR as a pre-screening method across a wide range of protein preservation levels. We analysed an extensive set of bones and teeth aged between ~100 to more than 1,000,000 years from >30 archaeological and palaeontological sites using NIR, chiral amino acid analysis, Fourier transform infrared spectroscopy (FTIR) and liquid chromatography tandem mass spectrometry (LC-MS/MS) and used this data to develop predictive NIR models. We compare the accuracy of the different screening methods for predicting successful data retrieval with LC-MS/MS, using Middle Pleistocene skeletal material from Tunel Wielki Cave, Poland (MIS 14 – 12) as a case study [5], a key site in European prehistory which has yielded Lower Palaeolithic artefacts. The results confirm the potential of non-destructive NIR screening of ancient skeletal material prior to palaeoproteomics, radiocarbon dating or isotopic analysis across a diverse range of environments and time periods.