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PubMed1997

Molecular cloning of cDNAs for two pro-phenol oxidase subunits from the malaria vector, Anopheles gambiae.

Phenol oxidase exists in insect hemolymph as a zymogen, pro-phenol oxidase (pro-PO), which is activated by specific proteolysis in response to infection or wounding. Phenol oxidase catalyses the synthesis of quinones that polymerize to form melanin deposits, which encapsulate parasites and help to seal wounds. Antibodies to pro-PO from Manduca sexta bound to 76, 72, and 71 kDa polypeptide bands from hemolymph of Anopheles gambiae larvae. This antiserum was used to screen a cDNA library from A. gambiae fourth-instar larvae. Full-length clones were isolated for two different pro-POs, designated A. gambiae proPO-p1 and proPO-p2, which are 67% identical in nucleotide sequence and 66% identical in deduced amino acid sequence. The A. gambiae pro-PO sequences are more similar to pro-PO from Drosophila melanogaster than to lepidopteran or crustacean pro-PO sequences in the GenBank database. Like the other arthropod pro-POs, the A. gambiae pro-PO sequences lack a signal peptide and have two conserved regions predicted to bind two copper atoms in the active site of the enzyme. The availability of these pro-PO cDNAs should be useful in examining the biochemical differences between A. gambiae strains that are refractory or susceptible to Plasmodium infection, and differ in their ability to encapsulate the parasites.

Amino Acid Sequence↗

PubMedDate not supplied

High-level expression of a mitochondrial enzyme, ornithine transcarbamylase from rat liver, in a baculovirus expression system.

The mitochondrial enzyme, ornithine transcarbamylase (OTC) from rat liver was expressed in Spodoptera frugiperda (Sf) insect cells using a baculovirus vector. When insect cells were infected with recombinant Autographica californica nuclear polyhedrosis virus (AcNPV) containing a cDNA encoding the precursor form of OTC (pOTC) inserted into the polyhedrin gene, they expressed catalytically active enzyme at levels of approximately 2.5 micrograms/10(6) cells. About 25% of the active enzyme was a novel, partially processed product of pOTC containing four extra amino acids at the amino terminus of OTC. The most abundant protein found in mitochondria from infected insect cells was the normal processing intermediate iOTC, which contains 8 extra amino acids at the amino terminus of OTC. Whereas this species, present at 20 micrograms/10(6) cells, was not active and did not bind the transition-state analog inhibitor of OTC, delta-PALO, the novel processing product did bind and was affinity-purified, along with mature OTC, on a PALO-affinity column. The OTC expressed in insect cells was located in the same compartment of the mitochondrion as in rat liver. The incomplete processing occurred in vitro in both noninfected and infected insect cells. The high level of expression of iOTC using the baculoviral expression system provides a means of overproducing an obligatory intermediate in the mitochondrial import process.

Amino Acid Sequence↗

PubMed1988

Overproduction of the protein encoded by the maize transposable element Ac in insect cells by a baculovirus vector.

The polypeptide encoded in the Activator (Ac) element of Zea mays L. has been expressed in Spodoptera frugiperda insect cells using plasmids which carry the strong polyhedrin promoter of the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV). Recombinant AcNPVs with the Ac-cDNA integrated and under the control of the viral polyhedrin promoter have been isolated and their genomes have been partly characterized as to the location of the foreign DNA insert. Upon infection of S. frugiperda cells with the recombinant AcNPV, maize Ac element specific messenger RNAs, as well as a newly synthesized polypeptide with an apparent molecular weight of about 116 kDa, have been detected in extracts of recombinant infected cells. This polypeptide is absent from extracts of wild-type infected cells expressing the polyhedrin polypeptide which can be recognized by the presence of nuclear inclusion bodies. Recombinant infected cells lack this protein. The Ac specific polypeptide is detected by antisera, which have been raised against fusion proteins containing Ac sequences synthesized in Escherichia coli, both in immunoprecipitation and in Western blotting experiments. The Ac specific protein is a nuclear phosphoprotein and represents about 1%-2% of the newly synthesized protein.

Animals↗

PubMed1963

DETERRENT EFFECT OF INSECTICIDES ON MALARIA VECTORS.

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Animals↗

PubMed1995

Assembly of the T = 4 Nudaurelia capensis omega virus capsid protein, post-translational cleavage, and specific encapsidation of its mRNA in a baculovirus expression system.

We have expressed the gene encoding the coat protein (CP) of Nudaurelia capensis omega virus in insect cells with a baculovirus vector. Expression of CP resulted in formation of virus-like particles (VLPs) having a size consistent with the T = 4 quasi-symmetry observed for native virions. This is the first demonstration of assembly for a T = 4 particle, with chemically identical subunits present in four distinct environments, by heterologous expression. Initial yields of VLPs were low, and an efficient one step nondenaturing procedure involving separation on discontinuous glycerol gradients was developed. Using this method, VLPs were obtained in quantities sufficient for further characterization. Electron microscopic observation revealed 40-nm particles that were morphologically similar to native virus. SDS-PAGE revealed that these particles were composed of a 62-kDa major protein and a minor 70-kDa protein. Pulse-chase experiments revealed that the larger species was processed into the smaller one very slowly over the course of an infection. It was also determined that this cleavage was apparently dependent on release of these particles from the cell. Furthermore, these particles were found to encapsidate the polyhedrin promoter-directed CP mRNA with an apparently striking degree of specificity and selectivity. This investigation establishes that a specific encapsidation signal exists within the CP coding sequences and that the components required for reconstructing most, if not all, steps in the morphogenesis of this virus can be accomplished in baculovirus-infected cells. The results presented here are consistent with the belief that similar biological strategies are utilized by T = 3 nodaviruses and T = 4 tetraviruses in particle assembly.

Animals↗

PubMedDate not supplied

[Prevention and control of malaria in pregnant women in an urban setting (Yaoundé, Cameroun)].

The aim of this study was to evaluate the methods of preventing malaria (chemoprophylaxis, vector control) and of fever management (presumptive treatment of malaria) used for pregnant women in Yaounde, Cameroon and to identify the most important factors for assessing these practices. The 221 women studied were selected by cluster sampling. All had made extensive use of health services during pregnancy and 77% were using chemoprophylaxis. The number of febrile episodes in pregnant women who claimed to have used chemoprophylaxis was not significantly different to that in the women who did not use it. However, the mean birth weight of the babies of women who had used chemoprophylaxis was significantly higher. The women did not systematically use vector control measures; 21% used insect repellents (electric plaques, coil burners) and 20% used aerosol insecticides. Only 10% of the women slept under simple, untreated mosquito nets and none used mosquito nets impregnated with insecticide. Fifty per cent of the women had at least one episode of fever during pregnancy and 77% were treated for presumed malaria. However, the treatment was not standardized and was unsuitable in a third of cases. Possible changes in the chemoprophylaxis strategy are discussed.

Adult↗

PubMed1962