The SARS-CoV-2 Spike Protein Receptor-Binding Domain Expressed in Rice Callus Features a Homogeneous Mix of Complex-Type Glycans.

The spike protein receptor-binding domain (RBD) of SARS-CoV-2 is required for the infection of human cells. It is the main target that elicits neutralizing antibodies and also a major component of diagnostic kits. The large demand for this protein has led to the use of plants as a production platform. However, it is necessary to determine the N -glycan structures of an RBD to investigate its efficacy and functionality as a vaccine candidate or diagnostic reagent. Here, we analyzed the N -glycan profile of the RBD produced in rice callus. Of the two potential N -glycan acceptor sites, we found that one was not utilized and the other contained a mixture of complex-type N -glycans. This differs from the heterogeneous mixture of N -glycans found when an RBD is expressed in other hosts, including Nicotiana benthamiana . By comparing the glycosylation profiles of different hosts, we can select platforms that produce RBDs with the most beneficial N -glycan structures for different applications.