REGULATION OF SORTING AND POST-GOLGI TRAFFICKING OF RHODOPSIN BY ITS C-TERMINAL SEQUENCE QVS(A)PA

Several mutations that cause severe forms of the human disease autosom al dominant retinitis pigmentosa cluster in the C-terminal region of r hodopsin. Recent studies have implicated the C-terminal domain of rhod opsin in its trafficking on specialized post-Golgi membranes to the ro d outer segment of the photoreceptor cell. Here we used synthetic pept ides as competitive inhibitors of rhodopsin trafficking in the frog re tinal cell-free system to delineate the potential regulatory sequence within the C terminus of rhodopsin and model the effects of severe ret initis pigmentosa alleles on rhodopsin sorting. The rhodopsin C-termin al sequence QVS(A)PA is highly conserved among different species. Pept ides that correspond to the C terminus of bovine (amino acids 324-348) and frog (amino acids 330-354) rhodopsin inhibited post-Golgi traffic king by 50% and 60%, respectively, and arrested newly synthesized rhod opsin in the trans-Golgi network. Peptides corresponding to the cytopl asmic loops of rhodopsin and other control peptides had no effect. Whe n three naturally occurring mutations: Q344ter (lacking the last five amino acids QVAPA), V345M, and P347S were introduced into the frog C-t erminal peptide, the inhibitory activity of the peptides was no longer detectable. These observations suggest that the amino acids QVS(A)PA comprise a signal that is recognized by specific factors in the trans- Golgi network. A lack of recognition of this sequence, because of muta tions in the last five amino acids causing autosomal dominant retiniti s pigmentosa, most likely results in abnormal post-Golgi membrane form ation and in an aberrant subcellular localization of rhodopsin.