Regulation of protein secretion through controlled aggregation in the endoplasmic reticulum

A system for direct pharmacologic control of protein secretion was developed to allow rapid and pulsatile delivery of therapeutic proteins. A protein was engineered so that it accumulated as aggregates in the endoplasmic reticulum. Secretion was then stimulated by a synthetic small-molecule drug that induces protein disaggregation. Rapid and transient secretion of growth hormone and insulin was achieved in vitro and in vivo. A regulated pulse of insulin secretion resulted in a transient correction of serum glucose concentrations in a mouse model of hyperglycemia. This approach may make gene therapy a viable method for delivery of polypeptides that require rapid and regulated delivery.     

Genetic and pharmacological suppression of oncogenic mutations in ras genes of yeast and humans

The activity of an oncoprotein and the secretion of a pheromone can be affected by an unusual protein modification. Specifically, posttranslational modification of yeast a-factor and Ras protein requires an intermediate of the cholesterol biosynthetic pathway. This modification is apparently essential for biological activity. Studies of yeast mutants blocked in sterol biosynthesis demonstrated that the membrane association and biological activation of the yeast Ras2 protein require mevalonate, a precursor of sterols and other isoprenes such as farnesyl pyrophosphate. Furthermore, drugs that inhibit mevalonate biosynthesis blocked the in vivo action of oncogenic derivatives of human Ras protein in the Xenopus oocyte assay. The same drugs and mutations also prevented the posttranslational processing and secretion of yeast a-factor, a peptide that is farnesylated. Thus, the mevalonate requirement for Ras activation may indicate that attachment of a mevalonate-derived (isoprenoid) moiety to Ras proteins is necessary for membrane association and biological function. These observations establish a connection between the cholesterol biosynthetic pathway and transformation by the ras oncogene and offer a novel pharmacological approach to investigating, and possibly controlling, ras-mediated malignant transformations.     

Long-term synaptic potentiation

Long-term synaptic potentiation (LTP) is a leading candidate for a synaptic mechanism of rapid learning in mammals. LTP is a persistent increase in synaptic efficacy that can be quickly induced. The biophysical process that controls one type of LTP is formally similar to a synaptic memory mechanism postulated decades ago by the psychologist Donald Hebb. A key aspect of the modification process involves the N-methyl-D-aspartate (NMDA) receptor-ionophore complex. This ionophore allows calcium influx only if the endogenous ligand glutamate binds to the NMDA receptor and if the voltage across the associated channel is also sufficiently depolarized to relieve a magnesium block. According to one popular hypothesis, the resulting increase in the intracellular calcium concentration activates protein kinases that enhance the postsynaptic conductance. Further biophysical and molecular understanding of the modification process should facilitate detailed explorations of the mnemonic functions of LTP.     

Observation of shoemaker-levy impacts by the galileo photopolarimeter radiometer

The Galileo Photopolarimeter Radiometer experiment made direct photometric observations at 678 and 945 nanometers of several comet Shoemaker-Levy 9 fragments impacting with Jupiter. Initial flashes occurred at (fragment G) 18 July 1994 07:33:32, (H) 18 July 19:31:58, (L) 19 July 22:16:48, and (Q1) 20 July 20:13:52 [equivalent universal time coordinated (UTC) observed at Earth], with relative peak 945-nanometer brightnesses of 0.87, 0.67, 1.00, and 0.42, respectively. The light curves show a 2-second rise to maximum, a 10-second plateau, and an accelerating falloff. The Q1 event, observed at both wavelengths, yielded a color temperature of more than 10,000 kelvin at its peak.     

A host-targeting signal in virulence proteins reveals a secretome in malarial infection

Malaria parasites secrete proteins across the vacuolar membrane into the erythrocyte, inducing modifications linked to disease and parasite survival. We identified an 11-amino acid signal required for the secretion of proteins from the Plasmodium falciparum vacuole to the human erythrocyte. Bioinformatics predicted a secretome of >320 proteins and conservation of the signal across parasite species. Functional studies indicated the predictive value of the signal and its role in targeting virulence proteins to the erythrocyte and implicated its recognition by a receptor/transporter. Erythrocyte modification by the parasite may involve plasmodial heat shock proteins and be vastly more complex than hitherto realized.