Rhodopsin determinants for transducin activation: a gain-of-function approach

Three cytoplasmic loops in the G protein-coupled receptor rhodopsin, C2, C3, and C4, have been implicated as key sites for binding and activation of the visual G protein transducin. Non-helical portions of the C2- and C3-loops and the cytoplasmic helix-8 from the C4 loop were targeted for a "gain-of-function" mutagenesis to identify rhodopsin residues critical for transducin activation. Mutant opsins with residues 140-148 (C2-loop), 229-244 (C3-loop), or 310-320 (C4-loop) substituted by poly-Ala sequences of equivalent lengths served as templates for mutagenesis. The template mutants with poly-Ala substitutions in the C2- and C3-loops formed the 500-nm absorbing pigments but failed to activate transducin. Reverse substitutions of the Ala residues by rhodopsin residues have been generated in each of the templates. Significant ( approximately 50%) restoration of the rhodopsin/transducin coupling was achieved with re-introduction of residues Cys140/Lys141 and Arg147/Phe148 into the C2 template. The reverse substitutions of the C3-loop residues Thr229/Val230 and Ser240/Thr242/Thr243/Gln244 produced a pigment with a full capacity for transducin activation. The C4 template mutant was unable to bind 11-cis-retinal, and the presence of Asn310/Lys311 was required for correct folding of the protein. Subsequent mutagenesis of the C4-loop revealed the role of Phe313 and Met317. On the background of Asn310/Lys311, the inclusion of Phe313 and Met317 produced a mutant pigment with the potency of transducin activation equal to that of the wild-type rhodopsin. Overall, our data support the role of the three cytoplasmic loops of rhodopsin and suggest that residues adjacent to the transmembrane helices are most important for transducin activation.     

A GPR-protein interaction surface of Gi(alpha): implications for the mechanism of GDP-release inhibition.

Proteins containing G-protein regulatory (GPR) motifs represent a novel family of guanine nucleotide dissociation inhibitors (GDIs) for G(alpha) subunits from the Gi family. They selectively interact with the GDP-bound conformation of Gi(alpha) and transducin-alpha (Gt(alpha)), but not with Gs(alpha). A series of chimeric proteins between Gi(alpha)(1) and Gs(alpha) has been constructed to investigate GPR-contact sites on G(alpha) subunits and the mechanism of GPR-protein GDI activity. Analysis of the interaction of two GPR-proteins-AGS3GPR and Pcp2-with the chimeric G(alpha) subunits demonstrated that the GPR-Gi(alpha)(1) interface involves the Gi(alpha)(1) switch regions and Gi(alpha)(1)-144-151, a site within the helical domain. Residues within Gi(alpha)(1)-144-151 form conformation-sensitive contacts with switch III, and may directly interact with a GPR-protein or form a GPR-binding surface jointly with switch III. The helical domain site is critical to the ability of GPR-proteins to act as GDIs. Our data suggest that a mechanism of the GDI activity of GPR-proteins is different from that of GDIs for monomeric GTPases and from the GDI-like activity of G(betagamma) subunits. The GPR-proteins are likely to block a GDP-escape route on G(alpha) subunits.     

Neuronal mitochondrial amelioration by feeding acetyl-L-carnitine and lipoic acid to aged rats

Brain function declines with age and is associated with diminishing mitochondrial integrity. The neuronal mitochondrial ultrastructural changes of young (4 months) and old (21 months) F344 rats supplemented with two mitochondrial metabolites, acetyl-L-carnitine (ALCAR, 0.2%[wt/vol] in the drinking water) and R-α-lipoic acid (LA, 0.1%[wt/wt] in the chow), were analysed using qualitative and quantitative electron microscopy techniques. Two independent morphologists blinded to sample identity examined and scored all electron micrographs. Mitochondria were examined in each micrograph, and each structure was scored according to the degree of injury. Controls displayed an age-associated significant decrease in the number of intact mitochondria (P = 0.026) as well as an increase in mitochondria with broken cristae (P < 0.001) in the hippocampus as demonstrated by electron microscopic observations. Neuronal mitochondrial damage was associated with damage in vessel wall cells, especially vascular endothelial cells. Dietary supplementation of young and aged animals increased the proliferation of intact mitochondria and reduced the density of mitochondria associated with vacuoles and lipofuscin. Feeding old rats ALCAR and LA significantly reduced the number of severely damaged mitochondria (P = 0.02) and increased the number of intact mitochondria (P < 0.001) in the hippocampus. These results suggest that feeding ALCAR with LA may ameliorate age-associated mitochondrial ultrastructural decay and are consistent with previous studies showing improved brain function.     

Tear lipocalin: potential for selective delivery of rifampin

The potential of ligand binding proteins as drug carriers and delivery systems has recently sparked great interest. We investigated the potential of tear lipocalin (TL) to bind the antibiotic, rifampin, and the environmental conditions for controlled release. To determine if TL binds rifampin, gel filtration was used to isolate protein fractions of tears. Rifampin was detected by absorbance spectroscopy in the elution fractions containing TL. The bound complex of rifampin-TL generates optical activity at about 360 nm, indicating a unique conformation at the binding site. Rifampin has a higher affinity for TL (Kd=128 microM) than albumin. Rifampin is released from the TL calyx in acidic conditions and is displaced by palmitic acid. Autooxidation of free rifampin begins in minutes but is delayed by at least 3 h in the presence of TL. These properties are conducive to stabilization and delivery of rifampin to tubercles that are acidic and rich in fatty acids. These studies show the potential of TL as a carrier for rifampin with controlled release to a targeted environment.     

A framework for scabies control

Scabies is a neglected tropical disease (NTD) that causes a significant health burden, particularly in disadvantaged communities and where there is overcrowding. There is emerging evidence that ivermectin-based mass drug administration (MDA) can reduce the prevalence of scabies in some settings, but evidence remains limited, and there are no formal guidelines to inform control efforts. An informal World Health Organization (WHO) consultation was organized to find agreement on strategies for global control. The consultation resulted in a framework for scabies control and recommendations for mapping of disease burden, delivery of interventions, and establishing monitoring and evaluation. Key operational research priorities were identified. This framework will allow countries to set control targets for scabies as part of national NTD strategic plans and develop control strategies using MDA for high-prevalence regions and outbreak situations. As further evidence and experience are collected and strategies are refined over time, formal guidelines can be developed. The control of scabies and the reduction of the health burden of scabies and associated conditions will be vital to achieving the targets set in WHO Roadmap for NTDs for 2021 to 2030 and the Sustainable Development Goals.     

Exposure of rainbow trout (Oncorhynchus mykiss) to magnetite (Fe3O4) nanoparticles in simplified food chain: Study on ultrastructural characterization

The widespread exposure of metallic nanoparticles to the aquatic ecosystem and its adverse impact on human life is the colossal concern worldwide. In view of this, this context was investigated to analyze microscopically the bioaccumulation and localization of magnetite (Fe₃O₄) nanoparticles in the cellular organelles of rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in aquatic conditions. Initially, Fe₃O₄ nanoparticles were absorbed on to Elodea (Elodea canadensis) and fed to molluscs (Melanopsis praemorsa). Fish were fed with the same molluscs, and then the intestines and liver were examined using light and transmission electron microscopy. Results showed that nanoparticles were present in the cytoplasm and other organelles of cells (mitochondrion and lysosome) by absorbing through microvilli of the epithelial cells of the tunica mucosa in the intestine. Further, nanoparticles passed through the vessels of the lamina propria of the tunica mucosa and reached to the sinusoids of the liver via blood circulation. It was then accumulated from the endothelium of the sinusoid to the cytoplasm of liver hepatocytes and to mitochondria and lysosome. The accumulation of nanoparticles in the epithelial cells, cytoplasm, mitochondria, and lysosome revealed the degree of transparency of the pattern with slight hesitation. In summary, this investigation contributed towards the understanding of the physiological effects of Fe₃O₄ nanoparticles on O. mykiss, which ascertains essentiality for sustainable development of nanobiotechnology in the aquatic ecosystem.     

Inhibition of GDP/GTP exchange on G alpha subunits by proteins containing G-protein regulatory motifs

A novel Galpha binding consensus sequence, termed G-protein regulatory (GPR) or GoLoco motif, has been identified in a growing number of proteins, which are thought to modulate G-protein signaling. Alternative roles of GPR proteins as nucleotide exchange factors or as GDP dissociation inhibitors for Galpha have been proposed. We investigated the modulation of the GDP/GTP exchange of Gialpha(1), Goalpha, and Gsalpha by three proteins containing GPR motifs (GPR proteins), LGN-585-642, Pcp2, and RapIGAPII-23-131, to elucidate the mechanisms of GPR protein function. The GPR proteins displayed similar patterns of interaction with Gialpha(1) with the following order of affinities: Gialpha(1)GDP > Gialpha(1)GDPAlF(4)(-) > or = Gialpha(1)GTPgammaS. No detectable binding of the GPR proteins to Gsalpha was observed. LGN-585-642, Pcp2, and RapIGAPII-23-131 inhibited the rates of spontaneous GTPgammaS binding and blocked GDP release from Gialpha(1) and Goalpha. The inhibitory effects of the GPR proteins on Gialpha(1) were significantly more potent, indicating that Gi might be a preferred target for these modulators. Our results suggest that GPR proteins are potent GDP dissociation inhibitors for Gialpha-like Galpha subunits in vitro, and in this capacity they may inhibit GPCR/Gi protein signaling in vivo.