Figure 3.

Quality control of newly synthesized OVA. Normal OVA is synthesized as a mono-N-glycosylated glycoprotein at Asn-292 and secreted. Alternatively, OVA is N-glycosylated at Asn-292 and Asn-311 to Di-OVA by a possible error of oligosaccharyl transferase (OSTase). Di-OVA undergoes site-specific de-N-glycosylation to form Mono-OVA (CHO-Asn-292/Asp-311) by PNGase HO. The de-N-glycosylated Di-OVA may either (i) re-enter into normal secretory pathway or (ii) render itself susceptible to intracellular degradative system, which is proposed for degradation of malfolded and/or unassembled proteins (48).