Cell-surface H+-ATP synthase as a potential molecular target for anti-obesity drugs

Here we show that the cell-surface expression of the alpha subunit of H(+)-ATP synthase is markedly increased during adipocyte differentiation. Treatment of differentiated adipocytes with small molecule inhibitors of H(+)-ATP synthase or antibodies against alpha and beta subunits of H(+)-ATP synthase leads to a decrease in cytosolic lipid droplet accumulation. Apolipoprotein A-I, which has been shown to bind to the ectopic beta-chain of H(+)-ATP synthase and inhibit the activity of cell-surface H(+)-ATP synthase, also was found to inhibit cytosolic lipid accumulation. These results suggest that the cell-surface H(+)-ATP synthase has a previously unsuspected role in lipid metabolism in adipocytes.     

Two isoforms of chicken melanopsins show blue light sensitivity

Melanopsin is a vertebrate non-visual opsin and functions as a circadian photoreceptor in mammalian retinas. Here we found the expression of two kinds of melanopsin genes in the chicken pineal gland and identified the presence of five isoforms derived from these two genes. Reconstitution of the recombinant proteins with 11-cis-retinal revealed that at least two of these melanopsin protein isoforms can function as blue-sensitive photopigments with absorption maxima at 476-484nm. These values are consistent with maximal sensitivities of action spectra determined from the physiological and behavioral studies on mammalian melanopsins. The melanopsin isoforms found in this study may function as pineal circadian photoreceptors.     

Natural variation of ebony gene controlling thoracic pigmentation in Drosophila melanogaster

We identified the causal genetic variation for the difference in the thoracic trident pigmentation intensity between two wild-derived strains of Drosophila melanogaster. It was found to be the difference in expression level of ebony, which codes for an enzyme in the melanin-synthesis pathway and has pleiotropic effects on vision and behavior.     

Heat shock protein 70 interacts with aquaporin-2 and regulates its trafficking

The trafficking of aquaporin-2 (AQP2) involves multiple complex pathways, including regulated, cAMP-, and cGMP-mediated pathways, as well as a constitutive recycling pathway. Although several accessory proteins have been indirectly implicated in AQP2 recycling, the direct protein-protein interactions that regulate this process remain largely unknown. Using yeast two-hybrid screening of a human kidney cDNA library, we have identified the 70-kDa heat shock proteins as AQP2-interacting proteins. Interaction was confirmed by mass spectrometry of proteins pulled down from rat kidney papilla extract using a GST-AQP2 C-terminal fusion protein (GST-A2C) as a bait, by co-immunoprecipitation (IP) assays, and by direct binding assays using purified hsc70 and the GST-A2C. The direct interaction of AQP2 with hsc70 is partially inhibited by ATP, and the Ser-256 residue in the AQP2 C terminus is important for this direct interaction. Vasopressin stimulation in cells enhances the interaction of hsc70 with AQP2 in IP assays, and vasopressin stimulation in vivo induces an increased co-localization of hsc70 and AQP2 on the apical membrane of principal cells in rat kidney collecting ducts. Functional knockdown of hsc70 activity in AQP2 expressing cells results in membrane accumulation of AQP2 and reduced endocytosis of rhodamine-transferrin. Our data also show that AQP2 interacts with hsp70 in multiple in vitro binding assays. Finally, in addition to hsc70 and hsp70, AQP2 interacts with several other key components of the endocytotic machinery in co-IP assays, including clathrin, dynamin, and AP2. To summarize, we have identified the 70-kDa heat shock proteins as a AQP2 interactors and have shown for hsc70 that this interaction is involved in AQP2 trafficking.     

Trivalent recognition unit of innate immunity system: crystal structure of trimeric human M-ficolin fibrinogen-like domain

Ficolins are a kind of pathogen-recognition molecule in the innate immune systems. To investigate the discrimination mechanism between self and non-self by ficolins, we determined the crystal structure of the human M-ficolin fibrinogen-like domain (FD1), which is the ligand-binding domain, at 1.9A resolution. Although the FD1 monomer shares a common fold with the fibrinogen gamma fragment and tachylectin-5A, the Asp-282-Cys-283 peptide bond, which is the predicted ligand-binding site on the C-terminal P domain, is a normal trans bond, unlike the cases of the other two proteins. The trimeric formation of FD1 results in the separation of the three P domains, and the spatial arrangement of the three predicted ligand-binding sites on the trimer is very similar to that of the trimeric collectin, indicating that such an arrangement is generally required for pathogen-recognition. The ligand binding study of FD1 in solution indicated that the recombinant protein binds to N-acetyl-d-glucosamine and the peptide Gly-Pro-Arg-Pro and suggested that the ligand-binding region exhibits a conformational equilibrium involving cis-trans isomerization of the Asp-282-Cys-283 peptide bond. The crystal structure and the ligand binding study of FD1 provide an insight of the self- and non-self discrimination mechanism by ficolins.     

Expression of TGFβ3 RNA during chick embryogenesis: a possible important role in cardiovascular development

Formin was originally isolated as the gene affected by the murine limb deformity (ld) mutations, which disrupt the epithelial-mesenchymal interactions regulating patterning of the vertebrate limb autopod. More recently, a rapidly growing number of genes with similarity to formin have been isolated from many different species including fungi and plants. Genetic and biochemical analysis shows that formin family members function in cellular processes regulating either cytokinesis and/or cell polarisation. Another common feature among formin family members is their requirement in morphogenetic processes such as budding and conjugation of yeast, establishment of Drosophila oocyte polarity and vertebrate limb pattern formation. Vertebrate formins are predominantly nuclear proteins which control polarising activity in limb buds through establishment of the SHH/FGF-4 feedback loop. Formin acts in the limb bud mesenchyme to induce apical ectodermal ridge (AER) differentiation and FGF-4 expression in the posterior AER compartment. Finally, disruption of the epithelial-mesenchymal interactions controlling induction of metanephric kidneys in ld mutant embryos indicates that formin might function more generally in transduction of morphogenetic signals during embryonic pattern formation. Received: 24 September 1998 / Accepted: 30 September 1998     

Chemo-enzymatic synthesis and structure-activity study of artificially N-glycosylated eel calcitonin derivatives with a complex type oligosaccharide

Starting from N-glycosylated eel calcitonin derivatives that contain an N-acetyl-D-glucosamine residue specifically at the 3rd, 14th, 20th or 26th amino acid residue, corresponding glycopeptides with a complex-type oligosaccharide attached to the respective amino acid residue were synthesized by means of a transglycosylation reaction catalyzed by an endo-beta-N-acetylglucosaminidase from Mucor hiemalis . The use of a recombinant enzyme and an excess of a glycosyl donor led to a yield in excess of 60%. Calcitonin derivatives containing truncated oligosaccharides were also prepared via digestion of the complex-type N-glycan with exoglycosidases. Using these N-glycosylated calcitonin derivatives, the effect of carbohydrate structure and glycosylation site on the three-dimensional structure and the biological activity of the peptide were studied. The conformation of the peptide backbone did not change irrespective of the carbohydrate structure or the glycosylation site. However, hypocalcemic activity, calcitonin-receptor binding activity and the biodistribution of the derivatives were affected by the glycosylation and were dependent on both the carbohydrate structure and the glycosylation site. Although the larger oligosaccharides tended to hinder receptor binding, the biodistribution altered by N-glycosylation appeared to enhance the hypocalcemic activity in some cases, and the magnitude of the effect was dependent on the site of glycosylation.