The recombinant human coronavirus HKU1 (isolate N1) (HCoV-HKU1) spike protein (S1 Subunit, His Tag) consists of 756 amino acids with a predicted molecular mass of 85.8 kDa. As a result of high glycosylation, the apparent molecular mass of the recombinant protein is approximately 130-140 kDa in SDS-PAGE under reducing conditions.