Parchment Glutamine Index (PQI): A novel method to estimate glutamine deamidation levels in parchment collagen obtained from low-quality MALDI-TOF data

Abstract

Parchment was used as a writing material in the Middle Ages and was made using animal skins by liming them with Ca(OH) 2 . During liming, collagen peptides containing Glutamine (Q) undergo deamidation resulting in a mass shift of 0.984 Da. Assessing the extent of deamidation can inform us about parchment production patterns and quality. In this study, we propose a simple three-step workflow, developed as an R package called MALDIpqi(), to estimate deamidation in parchment derived collagen using lowresolution MALDI-TOF spectra. After pre-processing raw spectra, we used weighted least-squares linear regression to estimate Q deamidation levels from the convoluted isotopic envelope for seven collagen-peptide markers. Finally, we employed a linear mixed effect model to predict the overall deamidation level of a parchment sample termed Parchment Glutamine Index (PQI). To test the robustness of the workflow, we applied MALDIpqi() to previously published ZooMS data generated from almost an entire library of the Cistercian monastery at Orval Abbey, Belgium. In addition to reliably predicting PQI, we observed interesting patterns pertaining to parchment production. MALDIpqi() holds excellent potential for biocodicological and other archaeological studies involving collagen, such as bone, but we also foresee its application in the food and biomedical industry.

Wheat-Based Glues in Conservation and Cultural Heritage: (Dis)solving the Proteome of Flour and Starch Pastes and Their Adhering Properties

“…However, research on bone collagen has shown that deamidation does not necessarily correlate with age but is instead dependent on environmental conditions . While little research has been done to understand the effect of ancient tanning methods on collagen deamidation, it has been shown that deamidation of parchment and other skin objects is more dependent on the production techniques and history of the objects than age. , Processes such as liming (dehairing), deliming, and tanning are done under alkali and acidic conditions. Vegetable-tanned leathers have a low pH, which could accelerate deamidation with time.…”

Artefact Profiling: Panomics Approaches for Understanding the Materiality of Written Artefacts

“…Nevertheless, it has recently been proposed to use the deamidation grade of glutamine for the calculation of a Parchment Glutamine Index (PQI). However, the focus is not on the time-dependent deamidation, but on the production process, in particular the liming with Ca(OH) 2 , the animal type used, and the thickness, since these factors also have an influence on the deamidation grade [ 166 ].…”