Febs Letters

doi: 10.1016/0014-5793(95)90005-5pmid: N/A

Atack, John R.; Broughton, Howard B.; Pollack, Scott J.

doi: 10.1016/0014-5793(95)00063-Fpmid: 7890024

Since lithium inhibits IMPase and modulates phosphatidylinositol (PtdIns) cell signalling at therapeutically relevant concentrations (0.5–1.0 mM), IMPase has attracted attention as a putative molecular target for lithium in the treatment of manic depression. IMPase is a homodimer, with each subunit organised in an αβαβα arrangement of α‐helices and β‐sheets, and this type of structure seems crucial to the two‐metal catalysed mechanism in which an activated water molecule serves as a nucleophile. Lithium appears to inhibit the enzyme following substrate hydrolysis by occupying the second metal binding site before the phosphate group can dissociate from its interaction with the site 1 metal. The understanding of IMPase structure and the mechanism of substrate hydrolysis and lithium inhibition should be useful in the development of novel inhibitors which may prove clinically useful in the treatment of manic depression.

Gorr, Sven-Ulrik; Darling, Douglas S.

doi: 10.1016/0014-5793(95)00142-Vpmid: 7890045

Endocrine and exocrine cells each contain a regulated and constitutive secretory pathway. The presence of two distinct secretory pathways in the same cell type requires a sorting step to direct secretory proteins to the correct pathway. It is thought that regulated secretory proteins contain a specific sorting signal. However, this signal has not been identified. Amino acid sequence comparisons have not revealed any significant similarity between different regulated secretory proteins, suggesting that the sorting signal does not consist of a conserved primary sequence. In the present report, we have analyzed the predicted secondary structures of regulated secretory proteins and identified an N‐terminal hydrophobic peak (NHP) which is located approximately from amino acids 9–26, overlaps with a predicted α‐helix and contains charged amino acid residues. This signal is present in regulated secretory proteins that exhibit an N‐terminal sorting sequence, but it is absent from constitutively secreted proteins and proteins where the sorting sequence is not located near the N‐terminus. It appears that the NHP is both necessary and sufficient for sorting of many secretory proteins to the regulated secretory pathway.

Majumder, Kumud; De Biasi, Mariella; Wang, Zhiguo; Wible, Barbara A.

doi: 10.1016/0014-5793(95)00120-Xpmid: 7890032

We report the cloning and functional expression of a novel K+ channel β‐subunit from human atrium, hKvβ3. hKvβ3 is highly homologous to the two β‐subunits cloned from rat brain, Kvβ1 and Kvβ2, but has an essentially unique stretch of 79 N‐terminal residues. Upon expression in Xenopus oocytes, hKvβ3 accelerates the inactivation of co‐injected hKv1.4 currents and induces fast inactivation of non‐inactivating co‐injected hKv1.5 currents. By contrast, hKvβ3 had no effect on hKv1.1, hKv1.2, or hKv2.1 currents. Thus, hKvβ3 represents a third type of K+ channel β‐subunit which modulates the kinetics of a unique subset of channels in the Kv1 subfamily.

Toh, Hiroyuki; Ichikawa, Atsushi; Narumiya, Shuh

doi: 10.1016/0014-5793(95)00129-Wpmid: 7890033

The amino acid sequences of the receptors for various prostaglandins, thromboxane and lipoxin, which belong to the rhodopsin family, were aligned, and a phylogenetic tree was constructed to infer the evolutionary history of the arachidonic acid cascade. The obtained tree suggested that the origin of the cyclooxygenase pathway was different from that of the lipoxygenase pathway. The receptors involved in the cyclooxygenase pathway constructed an independent cluster, but the lipoxin A4 receptor, which is involved in the lipoxygenase pathway, belonged to the cluster of peptide receptors. The primitive form of the cyclooxygenase pathway had been a signal transduction system composed of prostaglandin E2 and its receptor associated with cAMP metabolism.

de Cavanagh, Elena M.V.; Inserra, Felipe; Ferder, León; Romano, Luis; Ercole, Liliana; Fraga, César G.

doi: 10.1016/0014-5793(95)00137-Xpmid: 7890034

We have characterized the effect of angiotensin converting enzyme (ACE) inhibitors on the activity of CuZn‐superoxide dismutase (CuZn‐SOD), Mn‐superoxide dismutase (Mn‐SOD), catalase, and selenium‐dependent glutathione peroxidase (Se‐GPx). CF1 mice (4‐month‐old females) were administered water containing enalapril (20 mg/l) or captopril (50 mg/l), during 4 to 11 weeks. After 11 weeks, enalapril treatment caused an increase in the activity of CuZn‐SOD, Mn‐SOD and Se‐GPx, from 19 ± 4 to 46 ± 7, 2.1 ± 0.2 to 3.8 ± 0.2 units/mg protein and 27 ± 3 to 54 ± 3 milliunits/mg protein, respectively. After 11 weeks, captopril treatment increased the activities (P < 0.05) of CuZn‐SOD, MnSOD and Se‐GPx to 35 ± 4, 2.9 ± 0.2 units/mg protein, and 38 ± 2 milliunits/mg protein, respectively. Catalase activity was not affected by the treatments. These results suggest that ACE inhibitors may protect cell components from oxidative damage by increasing the enzymatic antioxidant defenses.

Gregory, Steven T.; Dahlberg, Albert E.

doi: 10.1016/0014-5793(95)00132-Spmid: 7890035

Mutations in the anticodon of tRNAGlu (UUC) were isolated or constructed and characterized for their ability to suppress cognate nonsense or missense mutations in vivo. The C36‐to‐A36 transversion mutation was isolated as an ochre and an amber suppressor, while the G36 transversion was selected as a CAG missense suppressor. tRNAGlu suppressors of an AAG missense mutation could not be isolated, and a U36 transition mutation introduced into tRNAGlu in vitro conferred no suppressor phenotype. Over‐expression of glutamyl‐tRNA synthetase did not increase the activity of the U36 mutant tRNAGlu, suggesting a defect at the level of translation rather than at the level of synthetase recognition.

Leroy, Arnaud; Lippens, Guy; Wieruszeski, Jean-Michel; Parra, Henri-Joseph; Fruchart, Jean-Charles

doi: 10.1016/0014-5793(95)00134-Upmid: 7890036

To elucidate the molecular details of the conformation of apolipoprotein AI (apo AI), we have developed an approach related to the solubilization of this protein in 30% n‐propanol. We have previously reported the promotion of a native‐like structure for apo AI solubilized in n‐propanol, as depicted by circular dichroism, fluorescence, and limited proteolytic digestion as compared to the lipid associated form of apo AI. In the present study, we labeled the Lys residues of apo AI with 13C by reductive methylation and used 13C NMR to confirm the formation of a native‐like structure of apo AI in this environment. Furthermore, by the above criteria (circular dichroism and 13C NMR) and by using urea and temperature as denaturing agents, we show that the denaturation of the native‐like structure of apo AI in n‐propanol is a biphasic process. These studies show that in 30% n‐propanol, apo AI contains two independently folded structural domains, of markedly different stabilities that might correspond to the amino‐terminal and the carboxy‐terminal halves of the molecule.

van 't Hof, Ron; de Kruijff, Ben

doi: 10.1016/0014-5793(95)00135-Vpmid: 7890037

The binding of the transit peptide (trfd) and precursor of the chloroplast protein ferredoxin (prefd) to large unilamellar lipid vesicles was investigated in relation to the lipid composition of the bilayer. Prefd binds with a dissociation constant of 0.27 μM to vesicles with a composition corresponding to the chloroplast envelope outer membrane. Binding is mediated by the transit sequence. From an analysis of binding to vesicles containing the individual lipid components it could be concluded that anionic lipids are mainly responsible for binding, emphasizing the importance of electrostatics for the transit sequence‐lipid interaction. Binding is also mediated by the specific chloroplast glycolipid monogalactosyldiacylglycerol. Monolayer experiments revealed that in this case a more extended domain of the transit sequence inserts into the lipid layer. Precursor binding does not result in a loss of vesicle barrier function. However, high concentrations of trfd do cause release of vesicle‐enclosed carboxyfluorescein. The results are discussed in the light of the chloroplast protein import process, with special emphasis on the role of monogalactosyldiacylglycerol.

Boiziau, Claudine; Debart, Françoise; Rayner, Bernard; Imbach, Jean-Louis; Toulme, Jean-Jacques

doi: 10.1016/0014-5793(95)00138-Ypmid: 7534237

Alpha‐beta chimeric 17‐mer oligodeoxyribonucleotides containing either 5, 10 or 15 beta nucleotides were synthesized. The stability of the RNA/chimera hybrids was only slightly affected by the alpha stretch and by the alpha‐beta link, as was the affinity of the Moloney Murine Leukemia Virus reverse transcriptase for the duplexes. All chimeras inhibited in vitro cDNA synthesis in a cell‐free system to various extent, via the degradation of the RNA target by RNase H.