Expression and characterization of peripherin/rds-rom-1 complexes and mutants implicated in retinal degenerative diseases.

Nearly 40 disease-linked mutations have been reported for peripherin/rds to date; heterologous expression in tissue culture cells offers a valuable means of efficiently characterizing the biochemical properties of the various mutants. Peripherin/rds is proposed to act as an essential structural element in outer segment disk morphogenesis, and a present transgenic mice offer the sole tractable system in which recombinant peripherin/rds may be examined functionally in situ. Because the generation and characterization of transgenic animals are both expensive and time consuming, heterologous expression in cultured cells offers an important and complementary means of addressing protein structure and function. The immunopurification and detection of the peripherin/rds-rom-1 complex are performed using specific immunochemical reagents, monoclonal and polyclonal antibodies, that are not commonly available. Several laboratories have developed antibodies to peripherin/rds and rom-1 in rabbits and mice, using a variety of immunogens: purified ROS membranes, purified E. coli fusion proteins, and synthetic peptides coupled to proteins. The C-terminal regions appear to be most highly antigenic, although antibodies have been generated to other regions as well. Regardless of their source, antibodies must be thoroughly characterized; specificity is often a function of solution conditions and must be determined empirically. The approach as described here has provided explanations for several instances of peripherin/rds-associated disease, including digenic RP linked to as L185P mutation, and adRP associated with C118/119del and C214S mutations. In addition, the R172W mutation, linked to macular dystrophy and preferential loss in cone function, is shown to behave normally with respect to biosynthesis and subunit assembly; it likely involves a more subtle functional defect that remains to be described. Finally, the methodology reported here has suggested the existence of a novel (homotetrameric) form of peripherin/rds in individuals lacking rom-1; this hypothesis has been confirmed in rom-1 knockout mice. The information obtained thus far demonstrates the utility of using heterologously expressed peripherin/rds and rom-1 to investigate the consequences of disease-linked mutations in these polypeptides. Heterologous cell expression coupled with transgenic mouse methodologies should continue to provide a more detailed understanding of molecular mechanisms underlying inherited retinal degenerative diseases.