Irisin is an exercise-induced myokine and has initially showed a promising function in browning white adipose tissue and increasing energy expenditure. The overall objective of the proposed project is to engineer irisin for uncovering its signaling in obesity, with the ultimate hope to capture its benefits for obesity prevention and treatment. The hypothesis is that physiological and pharmacological functions of irisin can be interpreted and controlled through identifying and targeting irisin receptor IR. Over the last awarding period, we have made several significant discoveries that partially test the hypothesis and achieve the objective. Specifically, we have identified a putative region for irisin-IR interactions and validated the involvement of this region through producing irisin mutants and examining their browning activity in 3T3-L1 adipocytes. We further attempted to use the yeast expression system to produce unnatural amino acid labelled irisin variants that expectedly capture the interactions between irisin and IR for IR identification. After extensive optimization of conditions in the yeast system, we later switched to the bacterial system and successfully produced such irisin variants. Finally, we used these variants to start the studies to capture IR. These results provided a solid foundation to accomplish proposed work in the next six months.