Peripherin/rds Influences Membrane Vesicle Morphology

Abstract

Peripherin/rds is an integral membrane glycoprotein found in the rim regions of vertebrate photoreceptor cell discs. Natural mutations of the encoding gene result in degenerative retinal disorders, such as retinitis pigmentosa. The retinal degeneration slow (rds) phenotype, observed in mice, is considered to be an appropriate model for peripherin/rds-mediated retinitis pigmentosa. Associated abnormalities in the outer segment of photoreceptor cells have implicated peripherin/rds in some aspect of disc morphology, yet it remains unclear whether such morphological effects are the cause or the result of this condition. Here we present the first direct evidence to support a role for peripherin/rds in maintaining the flattened vesicle morphology characteristic of photoreceptor outer segments. In vitro expression yields a 36-kDa immunoreactive species, which is inserted into membranes and undergoes N-glycosylation, inter-and intramolecular disulfide bonding, and dimerization. Electron microscopy reveals that peripherin/rds flattens microsomal vesicles. This effect appears to be dependent on disulfide bond formation but not N-glycosylation. The inability of two pathogenic peripherin/rds mutants (P216L and C165Y) to flatten membrane vesicles implicates such mutations as the primary cause of the retinal degeneration observed in retinitis pigmentosa.The outer segment of the vertebrate rod photoreceptor cell exhibits a highly specialized structure, comprised of a stack of 1000 or more flattened vesicles or discs (1). This organization is vital to the visual process, as it maximizes the area available for photoreception and allows efficient renewal of the photoreceptor outer segments. Any elements involved in the formation and maintenance of this structure are, therefore, of vital importance to the visual process. One protein that has been implicated to have such an involvement is peripherin/rds. Peripherin/rds is a 39-kDa integral membrane glycoprotein localized exclusively to the rim regions of photoreceptor cell discs (2, 3). A topological model has been proposed (4) in which the protein possesses four transmembrane helices and cytosolically oriented N and C termini. The protein has been shown to form disulfide-linked homodimers (2). These peripherin/rds dimers and homodimers of the related disc rim protein ROM-1 (5) are believed to non-covalently associate to form a functional heterotetrameric complex (6, 7).The clinical significance of the human peripherin/rds gene is illustrated by its involvement in a wide range of degenerative retinal disorders, including retinitis pigmentosa (8). To date, over 50 pathogenic mutations within the human gene have been identified. In addition there is a mutation in the murine gene that causes the related disorder, retinal degeneration slow (rds) (9). Phenotypically rds mice exhibit distinctive photoreceptor degeneration (10, 11), and hence, murine rds is considered an important animal model for the inherited human retinal degenerative condition. Mice homozygous for the rds condition ha...

Deletional Analysis of the Rod Photoreceptor Cell Peripherin/RDS Carboxy-Terminal Region

“…This is most likely due to the presence of both glycosylated and non-glycosylated forms. Others have observed similar doublet patterns under both in vivo (Boesze-Battaglia et al, 1997) and in vitro conditions (Wrigley et al, 2000). Collectively, these results suggest that the epitope tag does not interfere with protein expression or localization.…”

“…Although the function(s) of peripherin/rds remains elusive, it is proposed to serve an important role in the structural maintenance of rod and cone outer segments (Travis et al, 1991;Bascom et al, 1992;Goldberg et al, 1995). This is directly supported by in vitro studies showing that expression of peripherin/rds confers a flattened morphology upon microsomal membranes (Wrigley et al, 2000). More recently, Poetsch et al (2001) have shown that peripherin/rds interacts with glutamic acid rich proteins (GARP) associated with the β-subunit of the cGMP-gated channel located in ROS plasma membranes.…”

Differences in RDS trafficking, assembly and function in cones versus rods: insights from studies of C150S-RDS

“…Previous experiments support the role of C150 and higher order RDS oligomers in the disc-flattening process: in the absence of C150, vesicles lose flattened morphology and do not pinch into the characteristic rim structure (26). Consistent with the absence of ROM1 in RDS higher order oligomers, mice lacking ROM1 (rom1 2/2 ) exhibit no defects in flattening of the rim region (27).…”

Ubiquitously expressed secretory carrier membrane proteins (SCAMPs) 1-4 mark different pathways and exhibit limited constitutive trafficking to and from the cell surface

“…Finally, the short, poorly exposed and unglycosylated ectoplasmic loops linking transmembrane spans 1/2 and 3/4 distinguish the SCAMPs from other four-span transmembrane proteins (e.g. tetraspanins, physins, MAL proteolipids, claudins, occludins, connexins and peripherin) that have extended hydrophilic and often glycosylated loops, which in many cases mediate intermolecular interactions (Anderson et al, 2004;Hemler, 2003;Hubner et al, 2002;Martin-Belmonte et al, 2003;Sohl and Willecke, 2004;Wrigley et al, 2000).…”