Full-length soluble protein with foldon trimerization motif, mutated Furin recognition site and 6 stabilising mutations (F817P, A892 P, A899P, A942P, K986P and V987P), based on/modified from Amanat et al, 2020 (PMID: 32398876) and Hsieh et al, 2020 ( 1 * 100 µG