Challenging proteomic identification of animal species in historical leather from Japanese Samurai armors

This study reports a proteomic investigation of historical leather from four Japanese Samurai armors (16th-20th century) from the Morigi Collection (Lugano, Switzerland), with the aim of identifying the animal species used and gaining insight into historical craftsmanship, material selection, and later restoration practices. A bottom-up proteomic workflow combining MALDI-ToF-MS and RPLC-ESI-MS/MS was applied to six leather micro-samples. Initial analyses showed that conventional enzymatic digestion was ineffective for part of the dataset, likely because vegetable tanning agents formed stable insoluble complexes with collagen and hindered protein extraction. To overcome this limitation, an extraction protocol was optimized on modern vegetable-tanned leather using alkaline de-tanning, dialysis, and filter-aided sample preparation (FASP) prior to tryptic digestion. This workflow enabled the taxonomic assignment of all six historical specimens, including three samples that initially failed under conventional digestion and were only resolved after the optimized NaOH/FASP protocol. Deer hide was identified in one sample from the oldest armor, consistent with historical accounts of pre-modern Japanese leather use, whereas bovine leather was found in three samples and sheepskin in two others. The occurrence of sheepskin in a component associated with a 16th-century armor is difficult to reconcile with the documented history of animal exploitation in Japan and more plausibly suggests later undocumented restoration rather than original manufacture. Overall, the results demonstrate that bottom-up proteomics provides an effective and minimally invasive approach for the taxonomic identification of tanned historical leather and offers a robust analytical strategy for the study of culturally significant armor collections.