Characterization of a plant-produced recombinant human secretory IgA with broad neutralizing activity against HIV

Recombinant Secretory IgA (SIgA) complexes have the potential to improve antibody-based passive immunotherapeutic approaches to combat many mucosal pathogens. In this report, we describe the expression, purification and characterization of a human SIgA format of the broadly neutralizing anti-HIV monoclonal antibody (mAb) 2G12, using both transgenic tobacco plants and transient expression in Nicotiana benthamiana as expression hosts (P2G12 SIgA). The resulting heterodecameric complexes accumulated in intracellular compartments in leaf tissue, including the vacuole. SIgA complexes could not be detected in the apoplast. Maximum yields of antibody were 15.2 μg/g leaf fresh mass (LFM) in transgenic tobacco and 25 μg/g LFM after transient expression, and assembly of SIgA complexes was superior in transgenic tobacco. Protein L purified antibody specifically bound HIV gp140 and neutralised tier 2 and tier 3 HIV isolates. Glycoanalysis revealed predominantly high mannose structures present on most N-glycosylation sites, with limited evidence for complex glycosylation or processing to paucimannosidic forms. O-glycan structures were not identified. Functionally, P2G12 SIgA, but not IgG, effectively aggregated HIV virions. Binding of P2G12 SIgA was observed to CD209 / DC-SIGN, but not to CD89 / FcalphaR on a monocyte cell line. Furthermore, P2G12 SIgA demonstrated enhanced stability in mucosal secretions in comparison to P2G12 IgG mAb.     

Cytochrome bd biosynthesis in Escherichia coli: the sequences of the cydC and cydD genes suggest that they encode the components of an ABC membrane transporter

At least four genes are known to affect formation of the cytochrome bd-type terminal oxidase of Escherichia coli. In addition to the genes (cydA and cydB) encoding the two constituent subunits of this complex, a further two genes (cydC and cydD) map near 19 min on the E. coli chromosome. We report here the cloning of both genes on a 5.3 kb ClaI-HindIII restriction fragment, which, when used to transform either a cydC or cydD mutant, restored the ability of these mutants to grow on a selective medium containing azide and zinc ions and also restored the spectral signals associated with the cytochrome components of the oxidase complex. A subcloned 1.8 kb DdeI fragment similarly restored growth and cytochrome content of a cydD mutant, but not a cydC mutant. The complete nucleotide sequence of the ClaI-HindIII fragment reveals three open reading frames, one being trxB (19.3 min on the E. coli chromosome map, encoding thioredoxin reductase), confirming the mapping position of cydD previously established by P1-mediated transduction. Two ORFs identified by complementation experiments as cydD and cydC encode proteins with predicted molecular masses, respectively, of 65103 and 62 946 Da. The hydropathy profile of each protein reveals an N-terminal hydrophobic domain and a C-terminal hydrophilic domain containing a putative nucleotide-binding site. The gene products probably constitute an ABC (ATP-binding cassette) family membrane transporter, the function of which is necessary for the formation of the cytochrome bd quinol oxidase. The CydDC system appears to be the first prokaryotic example of a heterodimeric ABC transport system in which each polypeptide contains both hydrophobic and ATP-binding domains.     

Regeneration of neural crest derivatives in the <Emphasis Type="Italic">Xenopus</Emphasis>tadpole tail

Background  

After amputation of the Xenopus tadpole tail, a functionally competent new tail is regenerated. It contains spinal cord, notochord and muscle, each of which has previously been shown to derive from the corresponding tissue in the stump. The regeneration of the neural crest derivatives has not previously been examined and is described in this paper.