Interestingly, SARS and HKU1 (SI Fig. 2) S proteins did not exhibit specific mannose clusters that contribute to the overall mannose abundance, but only isolated glycans were underprocessed. We speculate that the oligomannose-type glycans here arise from protein-directed inhibition of glycan processing, as opposed to the glycan-influenced processing observed on MERS. Importantly, oligomannose-type glycans has also been implicated in innate immune recognition of coronaviruses by lectins47,48 that recognise these underprocessed glycans as pathogen-associated molecular patterns.