New Zealand produces large quantities of sheep pelts, which are largely used to make garment leather. Leather from conventionally processed sheep skins is not strong enough for footwear. Therefore, converting them to footwear leather would not only increase their raw material value but also be of more benefit to the NZ sheep leather industry as it targets the more stable footwear market rather than that of fashion-dependent clothing.

Although much research has been carried out into the physical structure and arrangement of collagen fibers/fibrils of leather and the effects of this on strength, the chemical characteristics and molecular composition of leather is less well understood.

It is known that raw sheep skins are strong but that their strength is lost in the process of leather making, which removes unwanted skin protein components in order to achieve desired properties, especially softness and flexibility in the leather. Using a proteomics approach would allow us to identify structural proteins in raw sheep skin. Comparing proteins from raw sheep skin to pickled sheep skin will give us information on what proteins have been lost during the leather process.

Here, we describe a survey of the identified skin proteome in raw and pickled sheep skins using a gel approach based on chip based nano-LC-MS/MS (Agilent Q-TOF 6520) and MALDI IMS (Autoflex III, Bruker). In the former method, solubilised skin proteins were separated by conventional 1D-gel electrophoresis prior to trypsin digestion. Trypsin digested peptides were then separated by nano-LC and identified using TPP (trans-proteomics pipeline), searching against the mammalian NCBI database. Protein matches were retained less than 5% FDR with at least two different unique peptides. The second method was an on-tissue approach applying trypsin directly on to the tissue sections. This is a powerful technique for mapping biological molecules such as endogenous proteins and peptides as it detects molecular species present and visualizes their distributions in a single tissue section. The two techniques combined provide us with high confidence in any identified proteins.