Soil proteomics: An assessment of its potential for archaeological site interpretation

Abstract

In this work, two sets of experiments were carried out to assess the potential of soil proteomics for archaeological site interpretation. First, we examined the effects of various protein isolation reagents and soil constituents on peptide mass fingerprinting (PMF) of soil-like materials spiked with bovine serum albumin (BSA). In a subsequent case study, we assessed the relative age of soils from an ancient clay floor of a Roman farmhouse using amino acid racemization and then applied MALDI-TOF–MS–MS to detect and identify biomarkers for human occupation. The results from the first experiments indicate that BSA isolation efficiencies are hampered by the presence of clays and reactive organic matter (glucose), whereas these effects are, to some extent, reversed by the presence of humic acids. We also show that specific regions of the BSA molecule (the out most α-helical regions of domain 2 and 3) are more susceptible to isolation than other regions and this suggest that soil proteins can be only partly isolated. Soil–protein interactions were also found to inhibit tryptic cleavage of BSA, resulting in an enhanced specificity of BSA peptides. Our results further stress the importance of multiple or sequential protein isolation protocols with a focus on citrate and hydrofluoric acid. Results from the case study indicate that the ancient floor samples contain degraded and most likely aged proteinaceous matter, probably of keratinaceous origin.