Synthetic ShK-like Peptide from the Jellyfish Nemopilema nomurai Has Human Voltage-Gated Potassium-Channel-Blocking Activity.

We identified a new human voltage-gated potassium channel blocker, NnK-1, in the jellyfish Nemopilema nomurai based on its genomic information. The gene sequence encoding NnK-1 contains 5408 base pairs, with five introns and six exons. The coding sequence of the NnK-1 precursor is 894 nucleotides long and encodes 297 amino acids containing five presumptive ShK-like peptides. An electrophysiological assay demonstrated that the fifth peptide, NnK-1, which was chemically synthesized, is an effective blocker of hKv1.3, hKv1.4, and hKv1.5. Multiple-sequence alignment with cnidarian Shk-like peptides, which have Kv1.3-blocking activity, revealed that three residues (3Asp, 25Lys, and 34Thr) of NnK-1, together with six cysteine residues, were conserved. Therefore, we hypothesized that these three residues are crucial for the binding of the toxin to voltage-gated potassium channels. This notion was confirmed by an electrophysiological assay with a synthetic peptide (NnK-1 mu) where these three peptides were substituted with 3Glu, 25Arg, and 34Met. In conclusion, we successfully identified and characterized a new voltage-gated potassium channel blocker in jellyfish that interacts with three different voltage-gated potassium channels. A peptide that interacts with multiple voltage-gated potassium channels has many therapeutic applications in various physiological and pathophysiological contexts.

Isolation and characterization of a mycovirus in Lentinula edodes.

A mycovirus was isolated from an edible mushroom, Lentinula edodes, that was suffering from a severe epidemic. Fractionation of the diseased cell extract by isopycnic centrifugation with 50% CsCl revealed that the diseased mushroom was infected by Lentinula edodes spherical virus (LeSV), a new spherical virus with a diameter of 55 nm. The particle of LeSV encapsidated the 12 kb RNA genome by a 120 kDa coat protein. BLAST analysis of the partially sequenced LeSV genome showed 95% sequence identity with a putative RNA-dependent RNA polymerase (RdRp) gene of the mycovirus HKB, which was previously reported as being a double-stranded RNA (dsRNA) element. In contrast to HKB, the RNA genome in LeSV is encapsidated by the 120 kDa coat protein. To confirm that the LeSV coat protein is encoded by the viral genome, the N-terminal amino acid sequence of the coat protein was determined. The resulting N-terminal amino acid sequence, N-SALDVAPVVPELYFXXLEV-C, was found to be located in the middle of the HKB ORF1, suggesting that the LeSV coat protein was indeed encoded by the virus. To detect LeSV in L. edodes, a primer set targeting the RdRp gene was designed based on the partial sequence of the LeSV genome. RT-PCR analysis showed that 56 of the 84 commercially available dikaryotic cultivars carry LeSV. The transmission pattern of the virus was determined by analysing basidiospores from LeSV-infected and LeSV-free fruiting bodies. Nine out of 10 basidiospores from the LeSV-infected cultivars contained the virus while the spores from the LeSV-free parent were free of LeSV, suggesting that vertical transmission is the primary mode of LeSV propagation.

Toxaphene affects the levels of mRNA transcripts that encode antioxidant enzymes in Hydra.

We evaluated toxaphene-induced acute toxicity in Hydra magnipapillata. The median lethal concentrations of the animals (LC(50)) were determined to be 34.5 mg/L, 25.0 mg/L and 12.0 mg/L after exposure to toxaphene for 24 h, 48 h and 72 h, respectively. Morphological responses of hydra polyps to a range of toxaphene concentrations suggested that toxaphene negatively affects the nervous system of H. magnipapillata. We used real-time quantitative PCR of RNA extracted from polyps exposed to two concentrations of toxaphene (0.3 mg/L and 3 mg/L) for 24 h to evaluate the differential regulation of levels of transcripts that encode six antioxidant enzymes (CAT, G6PD, GPx, GR, GST and SOD), two proteins involved in detoxification and molecular stress responses (CYP1A and UB), and two proteins involved in neurotransmission and nerve cell differentiation (AChE and Hym-355). Of the genes involved in antioxidant responses, the most striking changes were observed for transcripts that encode GPx, G6PD, SOD, CAT and GST, with no evident change in levels of transcripts encoding GR. Levels of UB and CYP1A transcripts increased in a dose-dependent manner following exposure to toxaphene. Given that toxaphene-induced neurotoxicity was not reflected in the level of AChE transcripts and only slight accumulation of Hym-355 transcript was observed only at the higher of the two doses of toxaphene tested, there remains a need to identify transcriptional biomarkers for toxaphene-mediated neurotoxicity in H. magnipapillata. Transcripts that respond to toxaphene exposure could be valuable biomarkers for stress levels in H. magnipapillata and may be useful for monitoring the pollution of aquatic environments.