Rhodopsin C-Terminal Sequence Qvs(A)Pa Directs Its Sorting To The Ros In Retinal Photoreceptors
Several mutations that cause severe forms of autosomal dominant retinitis pigmentosa (ADRP) cluster in the C-terminal region of rhodopsin. Recent studies have implicated the C-terminal domain of rhodopsin in its trafficking on specialized post-Golgi membranes to the rod outer segment (ROS) of the photoreceptor cell. In addition, aberrant subcellular localization of rhodopsin has been observed in transgenic animals carrying C-terminal mutations. To test if sequence within the C-terminal domain regulates rhodopsin sorting to the ROS, we tested the effects of synthetic peptides that mimic this domain on intracellular trafficking of rhodopsin reconstituted in the frog retinal cell free system. The rhodopsin C-terminal sequence QVS(A)PA is highly conserved among different species. Synthetic peptides corresponding to the C-terminal of frog (AA 330-354) and bovine (AA 324-348) rhodopsin inhibited post-Golgi trafficking by 60% and 50%, respectively, and arrested newly synthesized rhodopsin in the trans-Golgi network (TGN). Peptides corresponding to the cytoplasmic loops and several control peptides had no effect. To assess the role of the last 5 amino acids QVS(A)PA in rhodopsin trafficking, and to model three naturally occurring mutations: Q344ter (lacking the last 5 amino acids QVAPA), V345M and P347S, we introduced equivalent substitutions into the frog C-terminal peptide. Each of these substitutions completely abolished the inhibitory activity of the peptides. Our data could help to explain detrimental effect of mutant rhodopsin in patients with ADRP. We propose that amino acids QVS(A)PA comprise a sorting signal that is recognized by specific factor(s) in the trans-Golgi network. A lack of recognition of this sequence, due to mutations in the last five amino acids causing ADRP most likely results in abnormal post-Golgi membrane formation and in an aberrant subcellular localization of rhodopsin.
KeywordsRetinitis Pigmentosa Photoreceptor Cell Retinal Degeneration Cytoplasmic Loop Sorting Signal
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