Chapter 12 Zooarchaeology by Mass Spectrometry (Zooms) Collagen Fingerprinting for the Species Identification of Archaeological Bone Fragments
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Chapter 12 Zooarchaeology by Mass Spectrometry (ZooMS) Collagen Fingerprinting for the Species Identification of Archaeological Bone Fragments Michael Buckley 12.1 Introduction Bone is the most abundant organic tissue found typically to survive on archaeological sites, and in many cases can represent one of the most common types of find. Nonetheless, due to taphonomic and/or anthropologic factors, bone is more often than not fragmented beyond amenability to morphological identification. As a result, vast proportions of archaeological assemblages collected are often not uti- lized, and, therefore, the zooarchaeological inferences will undoubtedly be subject to some forms of bias. The objective identifications possible through the use of biomolecular information present in bone offer a tantalizing prospect for resolving such issues. The most obvious biomolecular target, ancient DNA (aDNA), has been, and continues to be, used (Burger et al. 2000; Horsburgh 2008; Waugh 2007) (see Matisoo-Smith, Chap. 11). However, this is not often a practical solution for appli- cation to the majority of assemblages given the high costs of analysis per sample, requirement for specialist facilities, and highly unpredictable likelihood of success. The success rates themselves are also increasingly poorer in warmer environments (Kahila Bar-Gal et al. 2002; Larson et al. 2007)—the environments more likely to have a wider range of wild taxa and be of greatest interest to those studying early animal husbandry. Recent years have witnessed the development of an alternative biomolecular method for species identification that addresses the impracticalities of the wide- spread adoption of aDNA-based methods. The method, described as a form of “Zooarchaeology by Mass Spectrometry” or ZooMS for short, is one that uses M. Buckley (*) Copyright © 2017. Springer. All rights reserved. © 2017. Springer. Copyright Manchester Institute of Biotechnology, University of Manchester, Manchester, UK e-mail: [email protected] © Springer International Publishing AG 2018 227 C.M. Giovas, M.J. LeFebvre (eds.), Zooarchaeology in Practice, https://doi.org/10.1007/978-3-319-64763-0_12 Zooarchaeology in Practice : Case Studies in Methodology and Interpretation in Archaeofaunal Analysis, edited by Christina M. Giovas, and Michelle J. LeFebvre, Springer, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/brown/detail.action?docID=5161630. Created from brown on 2018-02-26 15:54:58. 228 M. Buckley proteomics-based methods to analyze proteins that survive in faunal remains, pri- marily for species identification. The analysis of proteins rather than DNA has sev- eral advantages: (1) proteins are much more abundant (Tuross 1994; Tuross and Stathoplos 1993); (2) they survive for much longer periods of time (Rybczynski et al. 2013), making their analysis much more successful even in warmer environ- ments (Buckley et al. 2009, 2010); and (3) the analyses can be carried out at very low cost, often as low as the cost for aDNA screening methods themselves (e.g., amino acid racemization (Poinar et al. 1996) and carbon/nitrogen analysis (Götherström et al. 2002). In bone, the dominant protein is type I collagen, the protein that is typically referred to when describing the carbon source for radiocarbon dating and stable isotope analyses. Collagen is considered the most abundant protein in the vertebrate kingdom (Shoulders and Raines 2009) and is particularly abundant in the extracel- lular matrix (ECM). It has a wide range of functions that primarily relate to its role as a scaffold in bone mineral deposition. However, despite its presence in many different tissues and interactions with a wide range of other non-collagenous proteins (NCPs), in bone, collagen interacts with NCPs involved with the biomineralization pathway; the small mineral-binding protein osteocalcin is the most abundant of these NCPs in bone. Although many NCPs survive in archaeological bone for long periods of time, some of which are potentially more taxonomically informative (Buckley and Wadsworth 2014), collagen is by far the most abundant and will be the focus of this chapter. More than 28 types of collagen are known to exist within humans throughout the lifecycle (Ricard-Blum 2011), but 80–90% of the collagen in the body consists of types I, II, and III, of which type I collagen is by far the most abundant, as noted above. The triple helical structure common to all collagens is maintained through the presence of repeating imino acids, proline (Pro) and its modified form hydroxypro- line (Hyp), which induces the twisting structure in each of the three chains (Fig. 12.1 inset). However, to maintain this structure, the helix also requires the repeated pres- ence of glycine (Gly), the smallest amino acid, which typically occurs every three amino acids. Most other amino acids would not fit within this structure due to much larger side chains. As a result, collagen is known by its repeated Gly-Pro-Hyp motif and has largely been considered very highly conserved on the whole. Although some collagen types are homotrimers (i.e., formed from three identical chains), col- lagen type I is a heterotrimer, which in most vertebrates is made up of two identical chains called alpha 1 chains and one genetically distinct chain called the alpha 2 chain (hereafter referred to as α1(I) and α2(I) respectively). Notably, however, in actinopterygian (bony ray-finned) fish species, type I collagen is composed of three distinct chains, but the third (α3(I)) is a duplicate of the (α1(I)) gene (Morvan-Dubois et al. 2003). Recent research (e.g., Buckley et al. 2009) has found that the α2(I) is so much more variable that it does not appear to be restricted to the same requirement for Pro content, therefore making collagen much more useful for species identification than previously thought possible. Copyright © 2017. Springer. All rights reserved. © 2017. Springer. Copyright Zooarchaeology in Practice : Case Studies in Methodology and Interpretation in Archaeofaunal Analysis, edited by Christina M. Giovas, and Michelle J. LeFebvre, Springer, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/brown/detail.action?docID=5161630. Created from brown on 2018-02-26 15:54:58. 12 Zooarchaeology by Mass Spectrometry (ZooMS) Collagen Fingerprinting… 229 Fig. 12.1 Schematic of the two primary approaches to obtaining a collagen peptide mass fingerprint using either the soluble collagen or by heating and gelatinization of the insoluble collagen (scissors image sourced from www.commons.wikimedia.org, tube image sourced from www.clker.com); collagen triple helix shown in inset (image from 1BKV pdb file viewed online at http://www.rcsb. org/pdb/) Early developments of the ZooMS method started with the isolation of the collagen α2(I) telopeptide (Buckley et al. 2008) using solid phase extraction (SPE) cartridges following digestion with bacterial collagenase, but this single 18 amino acid peptide alone was not sufficient at separating all of the major domes- ticated animals. This was particularly problematic for sheep (Ovis aries) and goat (Capra hircus), whose skeletal elements are morphologically so similar that their separation is considered challenging (Zeder and Lapham 2010). As a result of this Copyright © 2017. Springer. All rights reserved. © 2017. Springer. Copyright morphological similarity, these two taxa have been typically reported together in Zooarchaeology in Practice : Case Studies in Methodology and Interpretation in Archaeofaunal Analysis, edited by Christina M. Giovas, and Michelle J. LeFebvre, Springer, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/brown/detail.action?docID=5161630. Created from brown on 2018-02-26 15:54:58. 230 M. Buckley zooarchaeological analyses as “caprine” or “ovicaprid”, despite the fact that their remains reflect distinct components of early animal husbandry based on differ- ences in animal behavior, diet, and habitat preferences. Subsequently, a similar SPE-based method following digestion with trypsin was developed to preferen- tially isolate a single large (33 amino acids) helical peptide from the α2(I) chain that could discriminate between these two taxa (Buckley et al. 2010), which was later verified by DNA analysis (Campana et al. 2013). Since then, the method was simplified into one that yielded two fractions for analysis, where the first fraction eluted with lower organic solvent concentration removed greater numbers of the typical collagen motif-containing peptides, and the second fraction with higher organic solvent concentration subsequently removed less typical collagen pep- tides from a specialist C18 pipette tip (Buckley et al. 2009). To date most applications to zooarchaeological studies have focused on mamma- lian taxa, with early work on domesticates (Buckley et al. 2009, 2010) followed more recently by studies on wild taxa (Buckley and Collins 2011), including marine mam- mals (Buckley et al. 2014). So far, little consideration has been given to the variability of amino acid sequences across a wider range of vertebrate taxa. This study explores in detail the information content potentially available through collagen sequence analysis, and considers the implications for the simplest form of ZooMS, the collagen fingerprint, given its amenability to high-throughput productivity and status as the most feasible molecular approach for widespread zooarchaeological application. A particular emphasis is placed on divergence times between vertebrate