Modulation of ecotropic murine retroviruses by N-linked glycosylation of the cell surface receptor/amino acid transporter.

The cell surface receptor for ecotropic host-range (infection limited to mice or rats) murine leukemia viruses (MuLVs) is the widely expressed system y+ transporter for cationic amino acids (CAT-1). Like other retroviruses, ecotropic MuLV infection eliminates virus-binding sites from cell surfaces and results in complete interference to superinfection. Surprisingly, infection causes only partial (ca 40 to 60%) loss of mouse CAT-1 transporter activity.

Kinetics and stoichiometry of a proton/myo-inositol cotransporter.

Voltage clamp recording was used to measure steady-state and presteady-state currents mediated by a myo-inositol transporter cloned from Leishmania donovani and expressed in Xenopus oocytes. Application of myo-inositol resulted in inward currents, which did not require external sodium and which were increased by increasing the extracellular proton concentration and by membrane hyperpolarization. Alkalinization of the extracellular space occurred concomitantly with myo-inositol influx.

Functional expression of a myo-inositol/H+ symporter from Leishmania donovani.

The vast majority of surface molecules in such kinetoplastid protozoa as members of the genus Leishmania contain inositol and are either glycosyl inositol phospholipids or glycoproteins that are tethered to the external surface of the plasma membrane by glycosylphosphatidylinositol anchors. We have shown that the biosynthetic precursor for these abundant glycolipids, myo-inositol, is translocated across the parasite plasma membrane by a specific transporter that is structurally related to mammalian facilitative glucose transporters. This myo-inositol transporter has been expressed and characterized in Xenopus laevis oocytes.

A family of putative receptor-adenylate cyclases from Leishmania donovani.

Leishmania parasites are exposed to pronounced changes in their environment during their life cycle as they migrate from the sandfly midgut to the insect proboscis and then into the phagolysosomes of the vertebrate macrophages. The developmental transformations that produce each life cycle stage of the parasite may be signaled in part by binding of environmental ligands to receptors which mediate transduction of extracellular signals. We have identified a family of five clustered genes in Leishmania donovani which may encode signal transduction receptors.

Characterization of Ca2+/calmodulin-dependent protein kinase IV. Role in transcriptional regulation.

We have characterized Ca2+/calmodulin-dependent protein kinase IV (CaM kinase IV), expressed using the baculovirus/Sf9 cell system, to assess its potential role in Ca2+-dependent transcriptional regulation. CaM kinase IV was strongly inhibited in vitro by KN-62, a specific CaM kinase inhibitor which suppresses Ca2+-dependent transcription of several genes, so we tested whether CaM kinase IV could stimulate transcription. Co-transfection of COS-1 cells by cDNA for CaM kinase IV gave 3-fold stimulation of a reporter gene expression, whereas co-transfection with CaM kinase II gave no transcriptional stimulation.