Endoplasmic reticulum-associated degradation (ERAD) of misfolded glycoproteins and mutant P23H rhodopsin in photoreceptor cells.
Membrane proteins, such as rhodopsin, often undergo N-linked glycosylation after translocation into the endoplasmic reticulum (ER). N-linked glycans are markers for correct protein folding, protein quality control, transport, and recognition by the ER-associated degradation (ERAD) machinery. The ER contains many resident proteins that promote correct folding of newly synthesized proteins and prevent inappropriate aggregation of protein-folding intermediates. The quality control mechanisms of the ER guarantee that only correctly folded proteins exit the ER and progress through the secretory pathway. Here, we review the ERAD pathway for glycoproteins and discuss recent reports linking ERAD to the development of retinitis pigmentosa arising from misfolded rhodopsin.