Biomedical subjects

R S Molday

Publications and source records attributed to R S Molday.

At least 55 records · Page 3Linked to original sources

PubMed1992

The cGMP-gated channel of rod outer segments is not localized in bipolar cells of the mammalian retina.

It has recently been suggested (Nature, 346 (1990) 269-271) that ON-bipolar cells express the same biochemical cascade and guanosine 3',5'-cyclic monophosphate (cGMP)-gated cation channel as rod outer segments. An antibody directed against the cGMP-gated channel of bovine rod outer segments was applied to cryostat sections of rat and cat retinae. No immunocytochemical labelling was found in bipolar cells. Therefore, if those cells express a cGMP-gated channel, it must be immunologically different to the 63 kDa protein constituting the cGMP-gated channel of the outer segment.

Animals↗

PubMed1992

Antibodies against synthetic peptides used to determine the topology and site of glycosylation of the cGMP-gated channel from bovine rod photoreceptors.

Peptides corresponding to amino acids 321-339 (peptide GS21) and 416-431 (peptide GS31) of the cGMP-gated channel from bovine rod photoreceptors were synthesized and used as antigens for the preparation of polyclonal antibodies. After affinity purification, both antipeptide antibodies were found to bind specifically to the channel protein after Western blotting, but only the antibody against GS21 gave satisfactory results on enzyme-linked immunosorbent assay and electron microscopy. Using immunocytochemistry, we were able to localize amino acids 321-339 to the extracellular side of the rod photoreceptor plasma membrane. By synthesizing heptapeptides corresponding to amino acids 324-330 (peptide GS2s) and 420-426 (peptide GS3s), we were able to affinity purify antibodies specific for two N-glycosylation consensus sites in the channel protein. As assessed by Western blotting, antibodies against GS3s were found to bind to both the glycosylated and deglycosylated channel proteins, whereas antibodies against GS2s only bound to the channel protein after enzymatic deglycosylation. Together, these results allow the refinement of folding models for the cGMP-gated channel and implicate Asn-327 as being the sole site of N-glycosylation.

Amino Acid Sequence↗

PubMed1992

Characterization and application of an in vitro detection system for studying the binding and phagocytosis of rod outer segments by retinal pigment epithelial cells.

Direct and indirect radioactivity and fluorescent assays have been developed to study the interaction of rod outer segments (ROS) with retinal pigment epithelial (RPE) cells. In the direct assays ROS labelled with 125I or fluorescein isothiocyanate (FITC) have been used to measure total phagocytosis, i.e. surface binding and ingestion. In the indirect assays RPE cells were first treated with unlabelled ROS or biotinylated ROS and subsequently probed with [125I]Rho 4D2 antirhodopsin antibody or [125I]streptavidin for radioactivity measurements or with the Rho 4D2 antibody and FITC-goat anti-mouse Ig or FITC-streptavidin for fluorescent counting. In these indirect methods the number of surface bound ROS were distinguished from the number of ingested ROS by comparative labelling of non-permeabilized and permeabilized ROS-treated RPE cells. Using these assays, we have studied the binding and ingestion of bovine ROS with cultured bovine RPE cells. As in the case of newborn cultured rat RPE cells [Hall and Abrams (1987) Exp. Eye Res. 45, 907-22], binding and ingestion of bovine ROS by bovine RPE cells was saturable with respect to ROS concentration and time. At 37 degrees C ROS binding reached a saturating concentration at 1 x 10(7) ROS per well; the number of bovine ROS ingested by bovine RPE cells, however, was less than the number of rat ROS ingested by rat RPE cells. When 1 x 10(7) ROS per well was used, maximal surface binding of bovine ROS to bovine RPE cells was obtained after 2-3 hr, whereas after an initial delay, ingestion rapidly increased to a maximum at 1-2 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Cloning of the cDNA for a novel photoreceptor membrane protein (rom-1) identifies a disk rim protein family implicated in human retinopathies.

The molecules essential to the continual morphogenesis and shedding of the opsin-containing disks of vertebrate photoreceptors are largely unknown. We describe a 37 kd protein, rom-1, which is 35% identical and structurally similar to peripherin/retinal degeneration slow (rds). Like peripherin, rom-1 is a retina-specific integral membrane protein localized to the photoreceptor disk rim. The two proteins are similarly oriented in the membrane, and each has a highly conserved (15/16 residues) cysteine- and proline-rich domain in the disk lumen. Although both rom-1 and peripherin form disulfide-linked dimers, they do not form heterodimers with each other, but appear to associate noncovalently. These results suggest both that rom-1 and peripherin are functionally related members of a new photoreceptor-specific protein family and that rom-1, like peripherin, is likely to be important to outer segment morphogenesis. The association of mutations in RDS with retinitis pigmentosa indicates that ROM1 is a strong candidate gene for human retinopathies.

Adult↗

PubMed1992

Transgenic mice with a rhodopsin mutation (Pro23His): a mouse model of autosomal dominant retinitis pigmentosa.

We inserted into the germline of mice either a mutant or wild-type allele from a patient with retinitis pigmentosa and a missense mutation (P23H) in the rhodopsin gene. All three lines of transgenic mice with the mutant allele developed photoreceptor degeneration; the one with the least severe retinal photoreceptor degeneration had the lowest transgene expression, which was one-sixth the level of endogenous murine rod opsin. Of two lines of mice with the wild-type allele, one expressed approximately equal amounts of transgenic and murine opsin and maintained normal retinal function and structure. The other expressed approximately 5 times more transgenic than murine opsin and developed a retinal degeneration similar to that found in mice carrying a mutant allele, presumably due to the overexpression of this protein. Our findings help to establish the pathogenicity of mutant human P23H rod opsin and suggest that overexpression of wild-type human rod opsin leads to a remarkably similar photoreceptor degeneration.

Animals↗

PubMed1992

Localization of peripherin/rds in the disk membranes of cone and rod photoreceptors: relationship to disk membrane morphogenesis and retinal degeneration.

The outer segments of vertebrate rod photoreceptor cells consist of an ordered stack of membrane disks, which, except for a few nascent disks at the base of the outer segment, is surrounded by a separate plasma membrane. Previous studies indicate that the protein, peripherin or peripherin/rds, is localized along the rim of mature disks of rod outer segments. A mutation in the gene for this protein has been reported to be responsible for retinal degeneration in the rds mouse. In the present study, we have shown by immunogold labeling of rat and ground squirrel retinas that peripherin/rds is present in the disk rims of cone outer segments as well as rod outer segments. Additionally, in the basal regions of rod and cone outer segments, where disk morphogenesis occurs, we have found that the distribution of peripherin/rds is restricted to a region that is adjacent to the cilium. Extension of its distribution from the cilium coincides with the formation of the disk rim. These results support the model of disk membrane morphogenesis that predicts rim formation to be a second stage of growth, after the first stage in which the ciliary plasma membrane evaginates to form open nascent disks. The results also indicate how the proteins of the outer segment plasma membrane and the disk membranes are sorted into their separate domains: different sets of proteins may be incorporated into membrane outgrowths during different growth stages of disk morphogenesis. Finally, the presence of peripherin/rds protein in both cone and rod outer segment disks, together with the phenotype of the rds mouse, which is characterized by the failure of both rod and cone outer segment formation, suggest that the same rds gene is expressed in both types of photoreceptor cells.

Animals↗

PubMed1992

Distribution of the Na(+)-Ca2+ exchange protein in mammalian cardiac myocytes: an immunofluorescence and immunocolloidal gold-labeling study.

The present study reports on the location of the Na(+)-Ca2+ exchanger in cardiac sarcolemma with immunofluorescence and immunoelectron microscopy. Both polyclonal and monoclonal antibodies to the Na(+)-Ca2+ exchanger were used. The mAb was produced from a hybridoma cell line generated by the fusion of mouse myeloma NS-1 cells with spleen cells from a mouse repeatedly immunized with isolated reconstituted canine cardiac Na(+)-Ca2+ exchanger (Philipson, K. D. S. Longoni, and R. Ward. 1988. Biochim. Biophys. Acta. 945:298-306). The polyclonal antibody has been described previously and reacts with three proteins (70, 120, 160 kD) in cardiac sarcolemma associated with the Na(+)-Ca2+ exchanger (Nicoll, D. A., S. Longoni, and K. D. Philipson. 1990. Science (Wash. DC). 250:562-565). Both the monoclonal and the polyclonal antibodies appear to react with extracellular facing epitopes in the cardiac sarcolemma. Immunofluorescence studies showed labeling of the transverse tubular membrane and patchy labeling of the peripheral sarcolemma. The immunofluorescent labeling clearly delineates the highly interconnected T-tubular system of guinea pig myocytes. This localization of the exchanger to the sarcolemma, with an apparent high density in the transverse tubules, was also seen with immunoelectron microscopy. It is of great interest that the Na(+)-Ca2+ exchanger, as the main efflux route for Ca2+ in heart cells, would be abundantly located in sarcolemma closest to the release of Ca2+.

Animals↗

PubMed1991

The cGMP-gated channel of the rod photoreceptor cell characterization and orientation of the amino terminus.

The molecular properties and orientation of the cGMP-gated cation channel of bovine rod outer segment membranes were studied using biochemical and immunochemical methods. Western blots labeled with anti-channel monoclonal antibodies indicate that the channel has a subunit Mr of 63,000 in bovine rod outer segment membranes prepared in the presence and absence of protease inhibitors and in rod outer segments from other mammalian retinas. The channel has an apparent Mr of 78,000 in both COS-1 cells and Xenopus oocytes expressing the cloned cDNA. NH2-terminal sequence analysis indicates that the lower Mr of the channel in rod outer segments is caused by the absence of the first 92 amino acids predicted by cDNA sequence analysis. Immunofluorescent and immunogold labeling has confirmed that the 63,000 form of the channel is present in rod outer segments. These results indicate that photoreceptor cell-specific co-translational or post-translational cleavage of the NH2-terminal segment of the channel occurs prior or during the incorporation of the channel into the rod outer segment plasma membrane. Immunogold labeling studies using site-directed antibodies also indicate that the NH2-terminal segment of the rod outer segment channel is exposed on the cytoplasmic side of the plasma membrane.

Amino Acid Sequence↗

PubMed1991

Glycolytic enzymes and a GLUT-1 glucose transporter in the outer segments of rod and cone photoreceptor cells.

The presence of glycolytic enzymes and a GLUT-1-type glucose transporter in rod and cone outer segments was determined by enzyme activity assays, glucose uptake measurements, Western blotting, and immunofluorescence microscopy. Enzyme activities of six glycolytic enzymes including hexokinase, phosphofructokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, and lactate dehydrogenase, were found to be present in purified rod outer segment (ROS) preparations. Immunofluorescence microscopy of bovine and chicken retina sections labeled with monoclonal antibodies against glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and lactate dehydrogenase have confirmed that these enzymes are present in rod and cone outer segments and not simply contaminants from the inner segments or other cells. Rod outer segments were also found to contain glucose transport activity as detected by 3-O-[14C]methylglucose uptake and exchange. The glucose transporter had a Km of 6.3 mM and a Vmax of 0.15 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for net uptake and a Km of 29 mM and a Vmax of 1.06 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for equilibrium exchange. These Km values for net uptake and equilibrium exchange are similar to values obtained for human red blood cells and are characteristic of GLUT-1-type glucose transporter. The transport was inhibited by both cytochalasin B and phloretin. Western blot analysis and immunofluorescence microscopy using type-specific glucose transporter antibodies indicated that both rod and cone outer segment plasma membranes have a GLUT-1 glucose transporter of Mr 45K as found in red blood cells and brain microsomal membranes. Solid-phase radioimmune competitive inhibition studies indicated that rod outer segment plasma membranes contained 15% the number of glucose transporters found in human red blood cell membranes and had an estimated density of 400 glucose transporter per micron2 of plasma membrane. These studies support the view that outer segments can generate energy in the form of ATP and GTP by anaerobic glycolysis to supply at least some of the energy requirements for phototransduction and other metabolic processes.

3-O-Methylglucose↗

PubMed1991

Photoreceptor peripherin is the normal product of the gene responsible for retinal degeneration in the rds mouse.

Retinal degeneration slow (rds) is a retinal disorder of an inbred strain of mice in which the outer segment of the photoreceptor cell fails to develop. A candidate gene has recently been described for the rds defect [Travis, G. H., Brennan, M. B., Danielson, P. E., Kozak, C. & Sutcliffe, J. G. (1989) Nature (London) 338, 70-73]. Neither the identity of the normal gene product nor its intracellular localization had been determined. We report here that the amino acid sequence of the bovine photoreceptor-cell protein peripherin, which was previously localized to the rim region of the photoreceptor disk membrane, is 92.5% identical to the sequence of the mouse protein encoded by the normal rds gene. The differences between the two sequences can be attributed to species variation. Monoclonal antibodies were used with Western blot analysis to localize the wild-type mouse peripherin/rds protein to isolated mouse rod outer segments and to show that it, like bovine peripherin, exists as two subunits linked by one or more disulfide bonds. The relative amounts of peripherin/rds protein and rhodopsin in retinal extracts of normal and rds mutant mice were also compared. Identification of peripherin as the protein encoded by the normal rds gene and its localization to membranes of rod outer segments will serve as a basis for studies directed toward defining the role of this protein in the morphogenesis and maintenance of the outer segment and toward understanding the mechanism by which the rds mutation causes retinal degeneration.

Amino Acid Sequence↗

PubMed1990

The cGMP-gated cation channel of bovine rod photoreceptor cells is associated with a 240-kDa protein exhibiting immunochemical cross-reactivity with spectrin.

A 240-kDa protein exhibiting immunochemical cross-reactivity with red blood cell spectrin has been shown to be directly associated with the 63-kDa cGMP-gated channel of bovine rod outer segments. When detergent-solubilized, chromatographically purified channel preparations were treated with Sepharose beads coupled to either an anti-240-kDa monoclonal antibody (PMs 4B2) or an anti-63-kDa channel monoclonal antibody (PMc 1D1), both the 240-kDa protein and the 63-kDa channel protein were concomitantly immunoprecipitated as analyzed by Western blotting of sodium dodecyl sulfate gels. Both of these antibody-Sepharose matrices also removed cGMP-gated channel activity as measured by functional reconstitution. In control studies anti-rhodopsin monoclonal antibody (Rho 1D4)-Sepharose beads removed residual rhodopsin, but not the 63/240-kDa complex or channel activity. Western blotting of purified rod outer segment disk and plasma membrane fractions and immunogold-dextran labeling of lysed rod outer segments indicated that the 240-kDa polypeptide, like the 63-kDa channel, is preferentially localized to the plasma membrane as visualized by electron microscopy. The 240-kDa protein does not appear to be directly involved in the cGMP-gated channel activity, but it may be part of a cytoskeletal system that serves to maintain the organization of the 63-kDa channel complex within the rod outer segment plasma membrane.

Animals↗

PubMed1990

Glyceraldehyde-3-phosphate dehydrogenase is a major protein associated with the plasma membrane of retinal photoreceptor outer segments.

A major 38-kDa protein associated with bovine rod outer segment plasma membranes, but not disk membranes, has been identified as glyceraldehyde-3-phosphate dehydrogenase on the basis of its N-terminal sequence and specific enzyme activity. This enzyme was extracted from lysed rod outer segments or isolated rod outer segment plasma membrane with 0.15 M NaCl and purified to homogeneity by affinity chromatography on a NAD(+)-agarose column. A specific activity of 90-100 units/mg of protein is within the range of activity obtained for glyceraldehyde-3-phosphate dehydrogenase isolated from other mammalian cells. Enzyme activity measurements indicate that this enzyme makes up approximately 2% of the total rod outer segment protein and over 11% of the plasma membrane protein. Protease digestion and binding studies on purified rod outer segment plasma and disk membranes suggest that glyceraldehyde-3-phosphate dehydrogenase reversibly interacts with a protease-sensitive plasma membrane-specific protein of rod outer segments. The finding that glyceraldehyde-3-phosphate dehydrogenase is present in large quantities in rod outer segments suggests that at least some of the energy required for the synthesis of ATP and GTP for phototransduction and other processes of the outer segment is derived from glycolysis which takes place within this organelle.

Amino Acid Sequence↗

PubMed1990

Molecular cloning, primary structure, and orientation of the vertebrate photoreceptor cell protein peripherin in the rod outer segment disk membrane.

Peripherin, a 39-kDa membrane protein, has been previously localized to the rim region of the vertebrate rod photoreceptor disk membrane by use of monoclonal antibodies and immunocytochemical labeling techniques. As an initial step in determining the structure and function of this protein, we have cloned and sequenced cDNA containing its complete coding sequence. A bovine retinal lambda gt11 expression library was screened with the antibodies, and a 583 base pair clone was initially isolated. The remaining part of the coding sequence was obtained from subsequent rescreenings of the same library and an independent lambda gt10 library. A C-terminal CNBr fragment of peripherin was purified by immunoaffinity chromatography and reverse-phase high-performance liquid chromatography. The amino acid sequence of the isolated C-terminal peptide and the N-terminal sequence analysis of immunoaffinity-purified peripherin are in agreement with the cDNA sequence. The cDNA sequence predicts that there are possibly four transmembrane domains. On the basis of immunocytochemical studies and sequence analysis, the hydrophilic C-terminal segment containing the antigenic sites for the antiperipherin monoclonal antibodies has been localized on the cytoplasmic side of the disk membrane. There are three consensus sequences for asparagine-linked glycosylation. Deglycosylation studies have indicated that at least one of these sites is utilized. The possible function of peripherin in relation to its primary structure is discussed.

Amino Acid Sequence↗

PubMed1990

Identification of the sodium-calcium exchanger as the major ricin-binding glycoprotein of bovine rod outer segments and its localization to the plasma membrane.

After neuraminidase treatment the Na+/Ca2+ exchanger of bovine rod outer segments was found to specifically bind Ricinus communis agglutinin. SDS gel electrophoresis and Western blotting of ricin-binding proteins purified from rod outer segment membranes by lectin affinity chromatography revealed the existence of two major polypeptides of Mr 215K and 103K, the former of which was found to specifically react with PMe 1B3, a monoclonal antibody specific for the 230-kDa non-neuraminidase-treated Na+/Ca2+ exchanger. Reconstitution of the ricin affinity-purified exchanger into calcium-containing liposomes revealed that neuraminidase treatment had no significant effect on the kinetics of Na+/Ca2+ exchange activation by sodium. We further investigated the density of the Na+/Ca2+ exchanger in disk and plasma membrane preparations using Western blotting, radioimmunoassays, immunoelectron microscopy, and reconstitution procedures. The results indicate that the Na+/Ca2+ exchanger is localized in the rod photoreceptor plasma membrane and is absent or present in extremely low concentrations in disk membranes, as we have previously shown to be the case for the cGMP-gated cation channel. Previous reports describing the existence of Na+/Ca2+ exchange activity in rod outer segment disk membrane preparations may be due to the fusion of plasma membrane components and/or the presence of contaminating plasma membrane vesicles.

Animals↗

PubMed1990

Role of the intradiscal domain in rhodopsin assembly and function.

The role of the intradiscal polypeptide loops in bovine rhodopsin has been investigated by deletions in the N-terminal tail and in loops B-C, D-E, and E-F as well as by single amino acid substitutions in the D-E loop. Mutants with three types of phenotypes were observed. Type I mutants showed a rhodopsin-like chromophore and glycosylation. Type II mutants did not regenerate the chromophore and showed abnormal glycosylation. Type III mutants showed poor chromophore regeneration and abnormal glycosylation. Reduced transducin activation was shown by some type I and III mutants. Single amino acid substitutions in the D-E loop gave mostly type I mutants. Deletions in loops B-C, D-E, and F-G gave type II mutants, whereas deletions in the N-terminal tail produced type III mutants. Systematic deletions of two adjacent amino acids in loop D-E indicated that the amino acid sequences 171-182 and 189-192 were essential to rhodopsin structure. Immunofluorescence double-staining and transmission electron microscopy of one type II mutant (with residues 189 and 190 deleted) showed that it was mostly in the endoplasmic reticulum, whereas the wild-type protein was in the plasma membrane. We conclude that the first step in the assembly of the rhodopsin molecule is the formation of a three-dimensional structure in the intradiscal domain involving the bulk of the out-of-the-membrane polypeptide segments followed by the linkage of Cys-110 and Cys-187 through a disulfide bond.

Amino Acid Sequence↗

PubMed1989

The cGMP-gated channel of bovine rod photoreceptors is localized exclusively in the plasma membrane.

Although there have been several reports pertaining to the existence of the cGMP-gated channel in the disk membrane of rod photoreceptors, its density there relative to that of the photoreceptor plasma membrane is unknown. Using immunoblotting, immunohistochemical, and reconstitution techniques on purified disk and plasma membrane preparations, we found that the density of channels in the plasma membrane was at least 50-fold higher than that of the disk membrane. Purification of membrane fractions without prior digestion of cytoskeletal components by mild trypsinization was found to increase the amount of channel protein present in disk membrane preparations. We propose that the presence of the channel protein in rod disk membrane preparations is an artifact arising from fusion of plasma membrane components during permeabilization of the photoreceptor cell.

Animals↗

PubMed1989

Study of airway epithelial permeability with dextran.

We studied the penetration of fluorescein isothiocyanate (FITC) T-40 dextran into the paracellular spaces in the tracheal mucosa and its appearance in the blood plasma of guinea pigs exposed to cigarette smoke or (controls) breathing room air. Under general anesthesia, the dextran solution was instilled onto the tracheal surface via a tracheotomy tube, arterial blood was sampled serially for 40 min, and then the trachea was fixed by perfusion or immersion. Examination of the tracheal mucosa with light microscopy, with and without epifluorescence, and transmission electron microscopy, revealed dextran in the paracellular spaces in mucosa from experimental animals but not controls. In all control animals, the levels of the dextran in plasma was below the sensitivity of the assay. By contrast, dextran levels in the plasma from the experimental animals fell within the sensitivity range of the assay and increased in blood at a rate of 0.00125 +/- 0.00023 (SE) expressed as a percentage of the instilled dose/min. We conclude that FITC T-40 dextran provides a reliable, fairly simple, fast method for assessing major, but not subtle, changes in paracellular permeability of the tracheal mucosa.

Animals↗

PubMed1988

Antigen-antibody interaction. Synthetic peptides define linear antigenic determinants recognized by monoclonal antibodies directed to the cytoplasmic carboxyl terminus of rhodopsin.

The specificities of four monoclonal antibodies rho 1D4, 1C5, 3A6, and 3D6 prepared by immunization of rod outer segments containing rhodopsin have been defined using synthetic peptides. All of these antibodies interact within the 18 residues at the COOH terminus of rhodopsin and recognize linear antigenic determinants of 4-11 residues. Twenty-seven synthetic peptide analogs of varying lengths of native sequence or containing single amino acid substitutions at each position of the COOH-terminal 18 residues have provided some insight into the mechanism of antigen-antibody binding. Our results clearly demonstrate that antibodies can be highly specific at key positions as shown by the loss of binding on single amino acid substitutions in the binding site. In contrast single amino acid substitutions at other positions in the binding site only affect affinity for some antibodies. Ionic interactions can dominate immunogenic determinants. Immunogenic determinants are not restricted to highly charged hydrophilic regions on the surface of a protein and may be dominated by hydrophobic interactions. Although certain side chains can dominate the interaction of the antigen with antibody, our results are in agreement with the interpretation that the free energies of all the contact points are additive and a certain free energy must be present to achieve binding. Antibodies with different specificities directed to the same region of the protein antigen can be produced in an immune response. Peptide antigens representing regions of a protein antigen bind best to the anti-protein antibody when the sequence is shortened to contain only those residues binding to the specificity site in the antibody. Cross-reactivity between protein antigens can be explained by conservation of the critical residues in the combining site.

Amino Acid Sequence↗