Comparative Analysis of Protein Glycosylation Pathways in Humans and the Fungal Pathogen Candida albicans
Figure 1
The N-glycosylation pathway. Commonalities and divergence in the N-linked glycosylation pathway. The shared structures between humans and Candida albicans have been colored, showing the rER synthesis of the Glc3Man9GlcNAc2 glycan and its transfer by the OST complex to a nascent protein. Once transferred, the Glc3Man9GlcNAc2 glycan is trimmed by the action of glucosidases and enters a quality control checkpoint performed by the CNX/CRT cycle. Once it passes this checkpoint, it is trimmed by mannosidase MAN1B1 to generate a Man8GlcNAc2 structure. At this point divergence occurs with C. albicans that synthesizes high-mannose glycans. In humans, the Man8GlcNAc2 structure is further demannosylated to Man5GlcNAc2 by Golgi mannosidases type I (MAN1A, MAN1B, and MAN1C). This N-linked glycan suffers further demannosylation and glycosylation processing by type II mannosidases (MAN2A1, MAN2A2), N-acetyl-galactosaminyl transferases (GlcNAcT), galactosyltransferases (GalT), fucosyltransferases (FUT) and sialyltransferases (STs). In humans, a glucosidase-independent trimming of Glc3Man9GlcNAc2 takes place, generating a Man8GlcNAc2 structure. In addition, lysosomal targeting of glycoproteins through modification with phosphate groups is only found in human cells.
