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Background: Foamy virus, which belong to the Spumaretrovirinae subfamily of Retroviridae, bridge the gap between Orthoretrovirinae and Hepadnaviridae, and display a long co-evolution with their hosts. Like other retroviruses, FVs encode a transactivator, Tas, which governs the levels of viral transcripts initiated through binding to the conserved promoters in 5’ long terminal repeat (LTR) and a unique internal promoter (IP). Unlike the other retrovirus, HIV, foamy viruses induced significant cytopathic effects in vitro, but has no significant disease association at the infection level in vivo. The characterization of regulator Tas in the Paradox of nonpathogenicity and cytopathic effects was still unknown.Results: Foamy virus separated from different hosts could form three groups which paralleled with the worldwide distribution of hosts due to geographical isolation. Although the physicochemical properties of different Tas were mainly in line with each other, the conserved motifs analyses still suggested divergences in protein functions. The proteins identified to interact with Tas of PFV, SFVora and SFVagm displayed that the three kinds of foamy viruses regulated different signal pathways and impacted virus-host immune interaction. Interestingly, predictions of interactional factors based on protein sequence showed USP7, a kind of deubiquitinating enzyme, could binding directly to Tas which led to its ubiquitin-dependent proteasome degradation. And this results also implyed that fomay virus could hijacked cytokine USP7 to stabilize the transcriptional activator Tas by de-ubiquitylation and thereby regulate the viral life cycle.Conclusion: Our experiments help to understand the survival strategy of foamy viruses in their hosts.

All scorpion toxins from different 30 species are simply reviewed. A new classification system of scorpion toxins is first proposed: scorpion toxins are classified into three families (long-chain scorpion toxins with 4 disulfide bridges, short-chain scorpion toxins with 3 disulfide bridges, and intermediate-type scorpion toxins with 3 or 4 disulfide bridges). Intermediate-type scorpion toxins provide a strong proof for the conclusion that channel toxins from scorpion venoms evolve from a common ancestor. Common organization of precursor nucleotides and genomic sequence, similar 3-dimensional structure, and the existence of intermediate type scorpion toxins and functionally intercrossing scorpion toxins show that all scorpion toxins affecting ion channels evolve from the common ancestor, which produce millions of scorpion toxins with function-diversity. © 2003 Wiley Periodicals, Inc. J Biochem Mol Toxicol 17:235–238, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.10083

Scorpion venom contains many small polypeptide toxins, which can modulate Na+, K+, Cl−, and Ca2+ ion–channel conductance in the cell membrane. A full-length cDNA sequence encoding a novel type of K+-channel toxin (named BmTxKS4) was first isolated and identified from a venom gland cDNA library of Buthus martensii Karsch (BmK). The encoded precursor contains 78 amino acid residues including a putative signal peptide of 21 residues, propeptide of 11 residues, and a mature peptide of 43 residues with three disulfide bridges. BmTxKS4 shares the identical organization of disulfide bridges with all the other short-chain K+-channel scorpion toxins. By PCR amplification of the genomic region encoding BmTxKS4, it was shown that BmTxKS4 composed of two exons is disrupted by an intron of 87 bp inserted between the first and the second codes of Phe (F) in the encoding signal peptide region, which is completely identical with that of the characterized scorpion K+-channel ligands in the size, position, consensus junctions, putative branch point, and A+T content. The GST-BmTxKS4 fusion protein was successfully expressed in BL21 (DE3) and purified with affinity chromatography. About 2.5 mg purified recombinant BmTxKS4 (rBmTxKS4) protein was obtained by treating GST-BmTxKS4 with enterokinase and sephadex chromatography from 1 L bacterial culture. The electrophysiological activity of 1.0μM rBmTxKS4 was measured and compared by whole cell patch-clamp technique. The results indicated that rBmTxKS4 reversibly inhibited the transient outward K+ current (Ito), delayed inward rectifier K+ current (Ik1), and prolonged the action potential duration of ventricular myocyte, but it has no effect on the action potential amplitude. Taken together, BmTxKS4 is a novel subfamily member of short-strain K+-channel scorpion toxin. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:187–195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20026