Solution structure of kurtoxin: a gating modifier selective for Cav3 voltage-gated Ca(2+) channels

Kurtoxin is a 63-amino acid polypeptide isolated from the venom of the South African scorpion Parabuthus transvaalicus. It is the first and only peptide ligand known to interact with Cav3 (T-type) voltage-gated Ca(2+) channels with high affinity and to modify the voltage-dependent gating of these channels. Here we describe the nuclear magnetic resonance (NMR) solution structure of kurtoxin determined using two- and three-dimensional NMR spectroscopy with dynamical simulated annealing calculations. The molecular structure of the toxin was highly similar to those of scorpion α-toxins and contained an α-helix, three β-strands, and several turns stabilized by four disulfide bonds. This so-called "cysteine-stabilized α-helix and β-sheet (CSαβ)" motif is found in a number of functionally varied small proteins. A detailed comparison of the backbone structure of kurtoxin with those of the scorpion α-toxins revealed that three regions [first long loop (Asp(8)-Ile(15)), β-hairpin loop (Gly(39)-Leu(42)), and C-terminal segment (Arg(57)-Ala(63))] in kurtoxin significantly differ from the corresponding regions in scorpion α-toxins, suggesting that these regions may be important for interacting with Cav3 (T-type) Ca(2+) channels. In addition, the surface profile of kurtoxin shows a larger and more focused electropositive patch along with a larger hydrophobic surface compared to those seen on scorpion α-toxins. These distinct surface properties of kurtoxin could explain its binding to Cav3 (T-type) voltage-gated Ca(2+) channels.     

Widdrol activates DNA damage checkpoint through the signaling Chk2–p53–Cdc25A–p21–MCM4 pathway in HT29 cells

Widdrol is an odorant compound isolated from Juniperus chinensis. We previously reported that widdrol induces Gap 1 (G1) phase cell cycle arrest and leads to apoptosis in human colon adenocarcinoma HT29 cells. It was also reported that this cell cycle arrest is associated with the induction of checkpoint kinase 2 (Chk2), p53 phosphorylation and cyclin dependent kinase (Cdk) inhibitor p21 expression. In this paper, we investigated the molecular mechanisms of widdrol on the activation of G1 DNA damage checkpoint at early phase when DNA damages occurred in HT29 cells. First of all, we examined that widdrol breaks DNA directly or not. As the results of DNA electrophoresis and formation of phosphorylated histone H2AX (γH2AX) foci in HT29 cells, widdrol generates DNA double-strand breaks directly within 0.5?h both in vitro and in vivo. Based on this result, the change of proteins related in checkpoint pathway was examined over a time course of 0.5-24?h. Treatment of HT29 cells with widdrol elicits the following: (1) phosphorylation of Chk2 and p53, (2) reduction of cell division cycle 25A (Cdc25A) expression, (3) increase of Cdk inhibitor p21 expression, and (4) decrease of the levels of Cdk2 and cyclin E expression in a time-dependent manner. Moreover, only the expression level of mini-chromosome maintenance 4 (MCM4) protein, a subunit of the eukaryotic DNA replicative helicase, is rapidly down-regulated in HT29 cells treated with widdrol over the same time course, but those of the other MCM proteins are unchanged. Overall, our results indicated that widdrol breaks DNA directly in HT29 cells, and this DNA damage results in checkpoint activation via Chk2-p53-Cdc25A-p21-MCM4 pathway and finally cells go to G1-phase cell cycle arrest and apoptosis.     

Design, synthesis and biological evaluation of 2-(substituted phenyl)thiazolidine-4-carboxylic acid derivatives as novel tyrosinase inhibitors

Herein we describe the design, synthesis and biological activities of 2-(substituted phenyl)thiazolidine-4-carboxylic acid derivatives as novel tyrosinase inhibitors. The target compounds 2a–2j were designed and synthesized from the structural characteristics of N-phenylthiourea, tyrosinase inhibitor and tyrosine, and l-DOPA, the natural substrates of tyrosinase. Among them, (2R/S,4R)-2-(2,4-dimethoxyphenyl)thiazolidine-4-carboxylic acid (2g) caused the greatest inhibition 66.47% at 20 μM of l-DOPA oxidase activity of mushroom tyrosinase. Kinetic analysis of tyrosinase inhibition revealed that 2g is a competitive inhibitor. We predicted the tertiary structure of tyrosinase, and simulated the docking of mushroom tyrosinase with 2g. These results suggest that the binding affinity of 2g with tyrosinase is high. Also, 2g effectively inhibited tyrosinase activity and reduced melanin levels in B16 cells treated with α-MSH. These data strongly suggest that 2g can suppress the production of melanin via the inhibition of tyrosinase activity.     

Comparison of Trophic Factors Changes in the Hippocampal CA1 Region Between the Young and Adult Gerbil Induced by Transient Cerebral Ischemia

In the present study, we investigated neuronal death/damage in the gerbil hippocampal CA1 region (CA1) and compared changes in some trophic factors, such as brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and vascular endothelial growth factor (VEGF), in the CA1 between the adult and young gerbils after 5?min of transient cerebral ischemia. Most of pyramidal neurons (89?%) were damaged 4?days after ischemia?Creperfusion (I?CR) in the adult; however, in the young, about 59?% of pyramidal neurons were damaged 7?days after I?CR. The immunoreactivity and levels of BDNF and VEGF, not GDNF, in the CA1 of the normal young were lower than those in the normal adult. Four days after I?CR in the adult group, the immunoreactivity and levels of BDNF and VEGF were distinctively decreased, and the immunoreactivity and level of GDNF were increased. However, in the young group, all of their immunoreactivities and levels were much higher than those in the normal young group. From 7?days after I?CR, all the immunoreactivities and levels were apparently decreased compared to those of the normal adult and young. In brief, we confirmed our recent finding: more delayed and less neuronal death occurred in the young following I?CR, and we newly found that the immunoreactivities of trophic factors, such as BDNF, GDNF, and VEGF, in the stratum pyramidale of the CA1 in the young gerbil were much higher than those in the adult gerbil 4?days after transient cerebral ischemia.     

Gliosis in the Mice Hippocampus Without Neuronal Death After Systemic Administration of High Dosage of Tetanus Toxin

Tetanus toxin (TeT), an exotoxin, has been studied to cause tetanus in mammalian brains, and it can block the release of some neurotransmitters and affect seizure propagation. In the present study, we investigated neuronal damage/death and glial changes in the mouse hippocampus after systemic administration (intraperitoneal injection) of TeT 10 and 100 ng/kg. In both the 10 and 100 ng/kg TeT-treated groups, no neuronal death occurred in any subregions of the mouse hippocampus until 24 h post-treatment; however, there were changes in glia in the hippocampus depending on time course and dosage. The morphology of GFAP-immunoreactive astrocytes and Iba-1-immunoreactive microglia was apparently changed in the 100 ng/kg TeT treated-group compared to the 10 ng/kg TeT treated-group. In the 100 ng/kg TeT treated-group, they were increased in size and their immunoreactivity was distinctively increased from 12 h post-treatment. We also found that their protein levels were increased in the hippocampus at 12 h post-treatment of 100 ng/kg TeT. In conclusion, these results indicate that the systemic administration of 100 ng/kg TeT induced a distinctive microglia changes in the mouse hippocampus without any neuronal death/damage.