11 research outputs found
Lightning discharges in association with mesospheric optical phenomena in Japan and their effect on the lower ionosphere
A quantitative and statistical analysis was performed using data from coordinated measurements consisting of ELF waves, VLF subionospheric disturbances and lightning discharges associated with transient luminous events(TLEs). These TLEs(sprites and elves) were observed during winter lightning storms over the Sea of Japan in the winter of 1998/99. A clear, straightforward relationship was found between the charge moment of the parent discharge, calculated from ELF(f<15Hz) transients, and the ionospheric disturbances, with a correlation coefficient of 0.97 independent of the type of TLEs; this suggests significant atmosphere-mesosphere-ionosphere coupling and implies that a large quasi-electrostatic(QE) field change occurring above lightning discharges with TLEs plays a significant role in modifying the electrical properties of the lower ionosphere. Sprites tend to be associated with large ionospheric disturbancs(-13~+ 4.6dB, compared with the unperturbed waves) and a large charge moment(260-875Ckm), whereas a relatively large lightning peak current(+223~+ 470kA,)(or a slow-tail amplitude) leading to a strong electromagnetic pulse(EMP) but with a rather small ionospheric disturbances seems to be necessary to initiate elves
Lightning discharges in association with mesospheric optical phenomena in Japan and their effect on the lower ionosphere
Antigen–Antibody Interactions and Structural Flexibility of a Femtomolar-Affinity Antibody
The femtomolar-affinity mutant antibody (4M5.3) generated
by directed
evolution is interesting because of the potential of antibody engineering.
In this study, the mutant and its wild type (4-4-20) were compared
in terms of antigen–antibody interactions and structural flexibility
to elucidate the effects of directed evolution. For this purpose,
multiple steered molecular dynamics (SMD) simulations were performed.
The pulling forces of SMD simulations elucidated the regions that
form strong attractive interactions in the binding pocket. Structural
analysis in these regions showed two important mutations for improving
attractive interactions. First, mutation of Tyr102(H) to Ser (sequence
numbering of Protein Data Bank entry 1FLR) played a role in resolving the steric
hindrance on the pathway of the antigen in the binding pocket. Second,
mutation of Asp31(H) to His played a role in resolving electrostatic
repulsion. Potentials of mean force (PMFs) of both the wild type and
the mutant showed landscapes that do not include obvious intermediate
states and go directly to the bound state. These landscapes were regarded
as funnel-like binding free energy landscapes. Furthermore, the structural
flexibility based on the fluctuations of the positions of atoms was
analyzed. It was shown that the fluctuations in the positions of the
antigen and residues in contact with antigen tend to be smaller in
the mutant than in the wild type. This result suggested that structural
flexibility decreases as affinity is improved by directed evolution.
This suggestion is similar to the relationship between affinity and
flexibility for in vivo affinity maturation, which was suggested by
Romesberg and co-workers [Jimenez, R., et al. (2003) <i>Proc.
Natl. Acad. Sci. U.S.A.</i> <i>100</i>, 92–97].
Consequently, the relationship was found to be applicable up to femotomolar
affinity levels
Bongkrekic acid as a selective activator of the peroxisome proliferator-activated receptor γ (PPARγ) isoform
Activation of the Long Terminal Repeat of Human Endogenous Retrovirus K by Melanoma-Specific Transcription Factor MITF-M12
The human and Old World primate genomes possess conserved endogenous retrovirus sequences that have been implicated in evolution, reproduction, and carcinogenesis. Human endogenous retrovirus (HERV)-K with 5′LTR-gag-pro-pol-env-rec/np9-3′LTR sequences represents the newest retrovirus family that integrated into the human genome 1 to 5 million years ago. Although a high-level expression of HERV-K in melanomas, breast cancers, and teratocarcinomas has been demonstrated, the mechanism of the lineage-specific activation of the long terminal repeat (LTR) remains obscure. We studied chromosomal HERV-K expression in MeWo melanoma cells in comparison with the basal expression in human embryonic kidney 293 (HEK293) cells. Cloned LTR of HERV-K (HML-2.HOM) was also characterized by mutation and transactivation experiments. We detected multiple transcriptional initiator (Inr) sites in the LTR by rapid amplification of complementary DNA ends (5′ RACE). HEK293 and MeWo showed different Inr usage. The most potent Inr was associated with a TATA box and three binding motifs of microphthalmia-associated transcription factor (MITF). Both chromosomal HERV-K expression and the cloned LTR function were strongly activated in HEK293 by transfection with MITF-M, a melanocyte/melanoma-specific isoform of MITF. Coexpression of MITF and the HERV-K core antigen was detected in retinal pigmented epithelium by an immunofluorescence analysis. Although malignant melanoma lines MeWo, G361, and SK-MEL-28 showed enhanced HERV-K transcription compared with normal melanocytes, the level of MITF-M messenger RNA persisted from normal to transformed melanocytes. Thus, MITF-M may be a prerequisite for the pigmented cell lineage-specific function of HERV-K LTR, leading to the high-level expression in malignant melanomas
Structure-Based Development of a Protein–Protein Interaction Inhibitor Targeting Tumor Necrosis Factor Receptor-Associated Factor 6
The
interactions between tumor necrosis factor (TNF) receptor-associated
factor 6 (TRAF6) and TNF superfamily receptors (TNFRSFs) are promising
targets for rheumatoid arthritis (RA) treatment. However, due to the
challenging nature of protein–protein interactions (PPIs),
a potent inhibitor that surpasses the affinity of the TRAF6–TNFRSF
interactions has not been developed. We developed a small-molecule
PPI inhibitor of TRAF6–TNFRSF interactions using NMR and in
silico techniques. The most potent compound, TRI4, exhibited an affinity
higher than those of TNFRSFs and competitively inhibited a TRAF6–TNFRSF
interaction. Structural characterization of the TRAF6–TRI4
complex revealed that TRI4 supplants key interactions in the TRAF6–TNFRSF
interfaces. In addition, some TRAF6–TRI4 interactions extend
beyond the TRAF6–TNFRSF interfaces and increase the binding
affinity. Our successful development of TRI4 provides a new opportunity
for RA treatment and implications for structure-guided development
of PPI inhibitors