ABSTRACT
Aggregated tau protein is associated with over 20 neurological disorders, which include Alzheimer's disease. Previous work has shown that tau's sequence segments VQIINK and VQIVYK drive its aggregation, but inhibitors based on the structure of the VQIVYK segment only partially inhibit full-length tau aggregation and are ineffective at inhibiting seeding by full-length fibrils. Here we show that the VQIINK segment is the more powerful driver of tau aggregation. Two structures of this segment determined by the cryo-electron microscopy method micro-electron diffraction explain its dominant influence on tau aggregation. Of practical significance, the structures lead to the design of inhibitors that not only inhibit tau aggregation but also inhibit the ability of exogenous full-length tau fibrils to seed intracellular tau in HEK293 biosensor cells into amyloid. We also raise the possibility that the two VQIINK structures represent amyloid polymorphs of tau that may account for a subset of prion-like strains of tau.
Subject(s)
Peptide Fragments/chemistry , Peptide Fragments/pharmacology , Protein Aggregates/drug effects , Protein Aggregation, Pathological/drug therapy , tau Proteins/chemistry , tau Proteins/metabolism , HEK293 Cells , Humans , Models, MolecularABSTRACT
The studies in this report were carried out to investigate the effects of delta 9-tetrahydrocannabinol (delta 9-THC) on cardiac membrane adenylate cyclase activity and to determine the role of changes in membrane lipid order in these effects. delta 9-THC and its psychoactive metabolite, 11-OH-delta 9-THC, increased isoproterenol (ISO) stimulation of adenylate cyclase in rat cardiac ventricular membranes. Cannabidiol, cannabinol and (+)-delta 9-THC were all without effect, indicating that this effect of delta 9-THC is stereoselective and specific for cannabinoids with psychoactive potency. delta 9-THC also increased glucagon stimulation of adenylate cyclase. The enhancement of both ISO and glucagon-stimulated adenylate cyclase was due to an increase in the Vmax of these agonists with no significant change in Kact. delta 9-THC did not affect basal adenylate cyclase activity or the activation of the enzyme by forskolin, guanine nucleotides or fluoride ion. Those cannabinoids which increased ISO-stimulated adenylate cyclase activity also decreased the break temperature of the Arrhenius plot; evidence that the effects of delta 9-THC involve changes in membrane phospholipid order. The effects of the cannabinoids on cardiac membrane phospholipid order were investigated directly using diphenylhexatriene fluorescence polarization. delta 9-THC and 11-OH-delta 9-THC alone decreased the break temperature of the diphenylhexatriene temperature profile, i.e., decreased the temperature of the lipid phase separation. This effect of delta 9-THC was stereoselective.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Adenylyl Cyclases/metabolism , Dronabinol/pharmacology , Heart/drug effects , Membrane Lipids/metabolism , Myocardium/enzymology , Animals , Colforsin/pharmacology , Enzyme Activation/drug effects , In Vitro Techniques , Male , Membrane Lipids/physiology , Rats , Rats, Inbred Strains , StereoisomerismABSTRACT
An immunocytochemical study was performed to localize the site of hemoglobin synthesis in larvae and embryos of the insect Chironomus thummi. Heterologous antisera specific for C. thummi hemoglobins were prepared using a highly purified hemoglobin extract. Tissue samples were prepared by glutaraldehyde fixation of whole dissected larvae or whole embryos without osmium tetroxide postfixation. Epoxy resin-embedded thin sections were labeled with a direct immunogold conjugate. Immune label was localized in rough endoplasmic reticulum of fat body cells of larvae. Immune label was also present in embryos. The technique, which did not require chemical etching of the sections, proved very useful for demonstration of this intracellular protein antigen.
