The Src family of tyrosine protein kinases in hemopoietic signal transduction.

The Src family of tyrosine protein kinases represent an expanding class of closely related intracellular enzymes that participate in the signal transduction pathways of a variety of surface receptors. One of the more surprising aspects of the information relating Src protein kinases to receptor signaling is the apparent diversity of receptor types with which the Src-related enzymes are reported to interact physically or functionally. Traditional biochemical and genetic approaches have yielded much information regarding the interactions between the Src tyrosine protein kinases and other cellular proteins in defined cell types, and emerging technologies, most notably homologous recombination in embryonal stem cells to achieve gene "knockouts," are providing new insights into the participation of the Src-related gene products in signal transduction and development.     

Changes in the activity and the polypeptide composition of the oxygen-evolving complex in photosystem II of tobacco leaves infected with cucumber mosaic virus strain Y.

The amount of 22- and 23-kDa polypeptides in a 23-kDa protein family, which plays a regulatory role in photosynthetic oxygen evolution, decreased significantly during the progress of appearance of chlorotic spots in cucumber mosaic virus strain Y (CMV[Y])-inoculated tobacco (Nicotiana tabacum 'Ky57') leaves (Plant Mol. Biol. 16:689-698, 1991). The present study was conducted to determine if the amount of other polypeptides of the oxygen-evolving complex and the oxygen-evolving activity also decreased in CMV(Y)-inoculated tobacco leaves. The amount of a 33-kDa polypeptide, which is essential to oxygen evolution, did not decrease in CMV(Y)-inoculated leaves showing early symptoms, although the amount of 22- and 23-kDa polypeptides began to decrease. However, comparative analysis of electron transport in thylakoid membranes indicated that the oxygen-evolving activity in CMV(Y)-inoculated tobacco leaves was only partly reduced, compared with the activity in CMV(O)-inoculated tobacco leaves which did not show clear symptoms. Partial inhibition of the oxygen-evolving activity, by a differential decrease in the amount of polypeptides of the oxygen-evolving complex, seems to be associated with the primary molecular process of symptom expression in CMV(Y)-inoculated tobacco leaves.     

Functional expression and CNS distribution of a beta-alanine-sensitive neuronal GABA transporter.

The synaptic action of gamma-aminobutyric acid (GABA) is terminated by high affinity, Na(+)-dependent transport processes in both neurons and glia. We have isolated a novel GABA transporter cDNA, GAT-B, which encodes a high affinity (Km = 2.3 microM), Na(+)- and Cl(-)-dependent GABA transport protein that is potently blocked by beta-alanine, a compound generally considered a selective inhibitor of glial transport. However, in situ hybridization studies indicate that GAT-B mRNA is expressed predominantly within neurons. These data indicate that the neuronal-glial distinction of GABA transporters based on inhibitor sensitivities must be reconsidered and suggest a greater diversity of GABA transporters than has been predicted by previous pharmacologic studies.     

In vivo biotinylation of fusion proteins expressed in Escherichia coli with a sequence of Propionibacterium freudenreichii transcarboxylase 1.3S biotin subunit.

Biotinylation of fusion proteins in E. coli was studied using a sequence of Propionibacterium freudenreichii transcarboxylase 1.3S biotin subunit. As the biotinylation sequence, we examined two sequences: one was of amino acid residues [84-123] of 1.3S, a partial sequence containing a region from a conserved tetrapeptide (Ala-Met-Bct-Met) around the biotinyl lysine (Bct) to the carboxyl terminal; the other was of an almost entire sequence [18-123]. We constructed recombinant plasmids for fusion proteins of beta-galactosidase, of chloramphenicol acetyltransferase, and of alkaline phosphatase. We found the biotinylation in the [18-123] sequence fused to alkaline phosphatase.     

A novel and efficient method for enzymatic synthesis of high purity maltose using moranoline (1-deoxynojirimycin).

A transglycosylation reaction with moranoline (1-deoxynojirimycin) was done with soluble starch as the glucosyl donor and Bacillus macerans amylase as a cyclodextrin glycosyltransferase [EC 2.4.1.19]. The resultant transglycosylation products with moranoline, obtained by treating the reaction mixture with a strong cation exchange resin, were hydrolyzed by beta-amylase [EC 3.2.1.2] from sweet potatoes. The hydrolysate was treated with a strong cation exchange resin, and high purity maltose was obtained.     

Development and testing of protocols for computer-aided design of peptide drugs, using oxytocin

Considerable clinical interest in neuropeptides and peptide hormones has stimulated recent research and development of peptide-based drugs. This process differs from most classical drug discovery procedures because peptide molecules have considerable inherent flexibility. In the present paper, to identify lowest energy and metastable conformers for drug design, and to develop protocols for such studies, conformational search algorithms, incorporating empirical energy calculations, have been applied in the analysis of the peptide oxytocin. Energy minimization in torsion angle space was carried out from a variety of starting conformations, including published structures, in all-atom mode and all with distance constraints for disulphide bond formation. The energy-minimized conformations have been further optimized by a mapping method. Complementary simulations have been performed in united-atom mode and a model representing the effects of water using dummy sites has been developed and tested for this representation. Several of the preferred conformers together with de novo conformations have been used as starting points in molecular dynamics simulations; 28 low potential energy conformations were located at a temperature of 4 K. Conformations are analysed to identify hydrogen bonds, phi-psi angle distributions and the RMS values relative to the X-ray structure of deamino-oxytocin. The modelled structure of lowest energy in the molecular mechanics calculations was also that of least RMS deviation from the crystal structure; whilst structures of lower energy but larger deviation were identified by molecular dynamics techniques. A metastable structure has been identified which satisfies existing criteria for the "active form", and this model is tested by a theoretical residue-substitution technique, to provide clues on the agonist/antagonist relationship at the atomic level.     

Human immunodeficiency virus type 1 envelope glycoproteins gp120 and gp160 induce interleukin-6 production in CD4+ T-cell clones.

Polyclonal B-cell activation is a characteristic feature of AIDS and of the AIDS-related complex. Since the immunoregulatory cytokine interleukin-6 (IL-6) plays a major role in inducing B-cell differentiation, we examined the effects of native human immunodeficiency virus type 1 envelope glycoproteins gp120 and gp160 on IL-6 induction. In this study, we have demonstrated that both gp120 and gp160 have the ability to induce IL-6 mRNA and biologically active IL-6 protein secretion in peripheral blood mononuclear cells in vitro. The envelope protein preparations had no detectable endotoxin as tested by the Limulus amebocyte lysate assay, and hence we can rule out the effect of contaminating endotoxin, which is a potent inducer of IL-6 in monocyte/macrophage cell cultures. In addition, we have shown that the envelope glycoproteins act directly on CD4(+)-cloned T cells to induce IL-6 production in the absence of monocytes. These findings indicate that monocytes and T cells both contribute to the secretion of IL-6, which plays an important role in the pathogenesis of B-cell activation in human immunodeficiency virus infection.     

Assembly and polarized release of Punta Toro virus and effects of brefeldin A.

Punta Toro virus (PTV), a member of the sandfly fever group of bunyaviruses, is assembled by budding at intracellular membranes of the Golgi complex. We have examined PTV glycoprotein transport, assembly, and release and the effects of brefeldin A (BFA) on these processes. Both the G1 and G2 proteins were transported out of the endoplasmic reticulum (ER) and retained in the Golgi complex in a stable structure, either during PTV infection or when expressed from a vaccinia virus recombinant. BFA treatment causes a rapid and dramatic change in the distribution of the G1 and G2 proteins, from a Golgi pattern to an ER pattern. The G1 and G2 proteins were found to be modified by medial but not trans Golgi network enzymes, in the presence or absence of BFA. We found that BFA blocks PTV release from cells but does not interfere with the intracellular assembly of infectious virions. Further, the BFA block of virus release is fully reversible, with high levels of virus release occurring upon removal of the inhibitor. It was also found that the release of PTV virions is polarized, occurring exclusively from the basolateral surfaces of the polarized Vero C1008 epithelial cell line.     

The antigen of hepatitis delta virus: examination of in vitro RNA-binding specificity.

The only known protein of hepatitis delta virus (HDV), the delta antigen, is found both within virus particles and within the nucleus of the infected cell, where it has one or more roles essential for RNA genome replication. Others have demonstrated that the antigen has the ability, in vitro, to specifically bind HDV RNA species. We report a further examination of this phenomenon, using partially purified recombinant protein, expressed as a fusion with the staphylococcal protein A. From Northwestern (RNA-immunoblot) analyses with both complete and various subdomains of HDV genomic and antigenomic RNAs, we found that a necessary feature for specific binding was that the RNA be able to fold to some extent into the so-called rodlike structure; this structure is a predicted intramolecular partial base-pairing of the circular RNA, with about 70% of all bases involved, so as to produce an unbranched rodlike structure. Six different subregions of the HDV rodlike structure, three on the genomic RNA and three on its complement, the antigenomic RNA, were tested and found to be sufficient for antigen binding. However, features in addition to the rodlike structure may also be necessary for specific binding, because we found that a similar structure present in the RNA of the potato spindle tuber viroid did not allow binding.     

Phosphorylation in the carboxyl-terminal domain of the capsid protein of hepatitis B virus: evaluation with a monoclonal antibody.

The capsid protein of hepatitis B virus (p21c) is made of 183 amino acids coded for by the C gene. By using p21c isolated from Dane particles (hepatitis B virus) as an immunogen, a monoclonal antibody (no. 2212) which recognized an epitope dependent on the phosphorylation of p21c was raised. The binding of no. 2212 antibody to authentic p21c was completely inhibited by a synthetic undecapeptide with a sequence of RRRSQSPRRRR, representing amino acids 165 to 175 of p21c, only when the peptide was phosphorylated. Either or both of Ser-168 and Ser-170 were phosphorylated in p21c in vivo, therefore, and contributed to the manifestation of the epitope. No. 2212 antibody bound to p21c from core particles derived from Dane particles or hepatocellular carcinoma tissues (PLC/342) propagated in nude mice but did not bind to p21c from core particles expressed in Escherichia coli or yeast cells, indicating different states of phosphorylation in them. Nonphosphorylated p21c showed a higher affinity for the viral DNA than did phosphorylated p21c. Since the serum from an asymptomatic carrier, with a high titer for antibody to hepatitis B core antigen, specifically bound to phosphorylated undecapeptide (amino acids 165 to 175), the epitope would stimulate humoral antibody responses in the human host.