Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect human cells by first attaching to the ACE-2 receptor via its receptor-binding domain (RBD) in the spike protein. We investigated the influence of N-glycosylation sites of the RBD and the membrane (M) protein on IgG antibody binding in serum samples from patients infected with the original SARS-CoV-2 strain in Germany. The N-glycosylation sites Asn331, Asn334, Asn343, Asn370 and Asn381 of RBDs of the wildtype, alpha, beta, gamma, kappa, and omicron BA.1 variants expressed in HEK293T and HEK293S GnTI- cells , as well as Asn5 for the M-protein were analyzed with tandem mass spectrometry for N-glycosylation.

In Escherchia coli, HEK293T and HEK293S GnTI- cells expressed RBD VOCs and in HEK293S GnTI- cells expressed M-protein were treated with Endoglycosidase F1 (removes N-glycans leaving a core N-acetylglucosamine) prior to filter-assisted sample preparation (FASP) with trypsin. Tryptic peptides were separated on a nanoUPLC system coupled to a ESI-IMS-Q-TOF-MS instrument. For data acquisition a HD-DDA approach created with MassLynx (version 4.2 SNC983) was used. Data analysis was done with Mascot Distiller (version 2.8.4.0) to generate mgf peak lists, which were searched with the Mascot search engine (version 2.87.0) using Mascot Daemon (version 2.6.0).

The following with Endoglycosidase F1 treated and trypsin digested samples were analyzed: HEK293S GnTI- cells expressed wildtype, alpha, beta, gamma, kappa RBD and M-protein, HEK293T cells expressed wildtype and omicron BA.1 RBD and Escherichia coli expressed wildtype RBD.