A plausible evolutionary scenario for the placement of N-GM in the ER. (IMAGE)
Caption
(a) Schematic representation of the NG pathway in bacteria and archaea. NG occurs on the cytoplasmatic side of the innermost cell membrane. After the glycan synthesis is completed on the membrane-bound lipid carrier the resulting glycan is enzymatically flipped to the periplasm or S-layer of bacteria and archaea. (b) The plausible invagination of the prokaryotic innermost membrane that contained N-GM. (c) If this forming vesicle pinched off the cell membrane, then the residing N-GM gains the spatial position identical to that present in the eukaryotic ER. (d) During eukaryogenesis new genes were added to the NG pathway which further process glycans inside the lumen of ER.
Credit
Domagoj Kifer et al.
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