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Biomedical subjects

D Raman

Publications and source records attributed to D Raman.

15 recordsLinked to original sources
PubMed1999

Binding of arrestin to cytoplasmic loop mutants of bovine rhodopsin.

The binding of arrestin to rhodopsin is a multistep process that begins when arrestin interacts with the phosphorylated C terminus of rhodopsin. This interaction appears to induce a conformational change in arrestin that exposes a high-affinity binding site for rhodopsin. Several studies in which synthetic peptides were used have suggested that sites on the rhodopsin cytoplasmic loops are involved in this interaction. However, the precise amino acids on rhodopsin that participate in this interaction are unknown. This study addresses the role of specific amino acids in the cytoplasmic loops of rhodopsin in binding arrestin through the use of site-directed mutagenesis and direct binding assays. A series of alanine mutants within the three cytoplasmic loops of rhodopsin were expressed in HEK-293 cells, reconstituted with 11-cis-retinal, prephosphorylated with rhodopsin kinase, and examined for their ability to bind in vitro-translated, 35S-labeled arrestin. Mutations at Asn-73 in loop I as well as at Pro-142 and Met-143 in loop II resulted in dramatic decreases in the level of arrestin binding, whereas the level of phosphorylation by rhodopsin kinase was similar to that of wild-type rhodopsin. The results indicate that these amino acids play a significant role in arrestin binding.

Amino Acid Sequence↗
PubMed1998

The cloning of GRK7, a candidate cone opsin kinase, from cone- and rod-dominant mammalian retinas.

PURPOSE: Desensitization in the rod cell of the mammalian retina is initiated when light-activated rhodopsin is phosphorylated by the G protein-coupled receptor kinase (GRK), GRK1, often referred to as rhodopsin kinase. A distinct kinase that specifically phosphorylates cone opsins in a similar manner has not been identified in mammals. To determine the existence of a cone opsin kinase, RNA from the retinas of cone- and rod-dominant mammals was analyzed by PCR. METHODS: RNA prepared from the retinas of two cone-dominant mammals, the thirteen-lined ground squirrel and the eastern chipmunk, and a rod-dominant mammal, the pig, was used to clone a new GRK family member by RT-PCR. The tissue distribution and localization of the kinase in retina were determined by Northern blot hybridization and in situ hybridization. The protein encoded by this cDNA was expressed in human embryonic kidney-293 (HEK-293) cells and compared with bovine GRK1 for its ability to phosphorylate bovine rhodopsin and to undergo autophosphorylation. RESULTS: The cDNA cloned from ground squirrel contains an open reading frame encoding a 548 amino-acid protein. Sequence analysis indicates that this protein is orthologous to GRK7 recently cloned from O. latipes, the medaka fish. Partial cDNA fragments of GRK7 were also cloned from RNA prepared from eastern chipmunk and pig retinas. In situ hybridization demonstrated widespread labeling in the photoreceptor layer of the ground squirrel retina, consistent with expression in cones. Recombinant ground squirrel GRK7 phosphorylates bovine rhodopsin in a light-dependent manner and can be autophosphorylated, similar to bovine GRK1. CONCLUSIONS: These results indicate that cone- and rod-dominant mammals both express GRK7. The presence of this kinase in cones in the ground squirrel and its ability to phosphorylate rhodopsin suggests that it could function in cone cells as a cone opsin kinase.

Amino Acid Sequence↗
PubMed1998

Rhodopsin arginine-135 mutants are phosphorylated by rhodopsin kinase and bind arrestin in the absence of 11-cis-retinal.

Arginine-135, located at the border between the third transmembrane domain and the second cytoplasmic loop of rhodopsin, is one of the most highly conserved amino acids in the family of G protein-coupled receptors. The effect of mutation at Arg-135 on the ability of rhodopsin to undergo desensitization was investigated. Four mutants, R135K, R135Q, R135A, and R135L, were examined for their ability to be phosphorylated by rhodopsin kinase, to bind arrestin, and to activate the rod cell G protein, transducin (Gt). All of the mutants were phosphorylated, bound arrestin, and were able to activate Gt when reconstituted with 11-cis-retinal. Surprisingly, several of the mutants could be phosphorylated by rhodopsin kinase and could bind arrestin in the absence of 11-cis-retinal but were not able to activate Gt. These observations represent the first demonstration of a mutant G protein-coupled receptor that assumes a conformation able to interact with its G protein-coupled receptor kinase and arrestin, but not with its G protein, in the absence of ligand.

Animals↗
PubMed1983

Acute knee joint rupture--a report of two unusual cases.

An acute rupture of the knee joint is a well recognized and documented condition. The symptoms and signs it produces have been described as the pseudothrombophlebitis syndrome and its importance in the differential diagnosis of calf pain is being increasingly recognized. We report two cases where the symptomatology has been unusual and stress the need for considering this condition in other atypical cases of leg pain which may not strictly conform in presentation to the pseudothrombophlebitis syndrome.

Acute Disease↗
PubMed1982

Trochanteric bursitis--a frequent cause of 'hip' pain in rheumatoid arthritis.

One hundred consecutive patients with rheumatoid arthritis (RA) were examined for the presence of trochanteric bursitis. This condition was found in 15. Ten patients responded to a single local injection of corticosteroid and the remaining 5 to a second injection. Trochanteric bursitis is an underdiagnosed, easily remediable cause of pain in RA. Specific examination for in presence should be a routine in all patients with RA, especially those with hip pain.

Arthritis, Rheumatoid↗
PubMed1981

Chondromalacia of the patella: an unusual presentation.

A 38-year-old male with a 10-year history of recurrent ruptured popliteal cyst at the right knee was diagnosed at arthroscopy to have chondromalacia patellae. After shaving of the affected area he had no further symptoms on follow-up 18 months later.

Adult↗
PubMed1981

Coexistent rheumatoid arthritis and tophaceous gout: a case report.

Rheumatoid arthritis and gout are both common rheumatic diseases, but their coincidence is rare. We report the case of a 67-year-old Caucasian woman with rheumatoid arthritis who later developed tophaceous gout. The tophi disappeared with remarkable rapidity on treatment with allopurinol.

Aged↗