Unusual Mechanism (unusual + mechanism)

Distribution by Scientific Domains

Selected Abstracts

Giant Room,Temperature Magnetodielectric Response in the Electronic Ferroelectric LuFe2O4

A. Subramanian
A very large drop in dielectric constant upon application of small magnetic fields is observed at room temperature for LuFe2O4 (see figure). Such behavior is unprecedented and indicates a strong coupling of spins and electric dipoles at room temperature. This behavior of LuFe2O4 is apparently related to its ferroelectricity, which occurs through the highly unusual mechanism of Fe2+ and Fe3+ ordering. [source]

External K+ modulates the activity of the Arabidopsis potassium channel SKOR via an unusual mechanism

Ingela Johansson
Summary Plant outward-rectifying K+ channels mediate K+ efflux from guard cells during stomatal closure and from root cells into the xylem for root,shoot allocation of potassium (K). Intriguingly, the gating of these channels depends on the extracellular K+ concentration, although the ions carrying the current are derived from inside the cell. This K+ dependence confers a sensitivity to the extracellular K+ concentration ([K+]) that ensures that the channels mediate K+ efflux only, regardless of the [K+] prevailing outside. We investigated the mechanism of K+ -dependent gating of the K+ channel SKOR of Arabidopsis by site-directed mutagenesis. Mutations affecting the intrinsic K+ dependence of gating were found to cluster in the pore and within the sixth transmembrane helix (S6), identifying an ,S6 gating domain' deep within the membrane. Mapping the SKOR sequence to the crystal structure of the voltage-dependent K+ channel KvAP from Aeropyrum pernix suggested interaction between the S6 gating domain and the base of the pore helix, a prediction supported by mutations at this site. These results offer a unique insight into the molecular basis for a physiologically important K+ -sensory process in plants. [source]

Crystallization and preliminary crystallographic analysis of the transcriptional regulator RfaH from Escherichia coli and its complex with ops DNA

Marina N. Vassylyeva
The bacterial transcriptional factor and virulence regulator RfaH binds to rapidly moving transcription elongation complexes through specific interactions with the exposed segment of the non-template DNA strand. To elucidate this unusual mechanism of recruitment, determination of the three-dimensional structure of RfaH and its complex with DNA was initiated. To this end, the Escherichia coli rfaH gene was cloned and expressed. The purified protein was crystallized by the sitting-drop vapor-diffusion technique. The space group was P6122 or P6522, with unit-cell parameters a = b = 45.46, c = 599.93,. A complex of RfaH and a nine-nucleotide oligodeoxyribonucleotide was crystallized by the same technique, but under different crystallization conditions, yielding crystals that belonged to space group P1 (unit-cell parameters a = 36.79, b = 44.01, c = 62.37,, , = 80.62, , = 75.37, , = 75.41). Complete diffraction data sets were collected for RfaH and its complex with DNA at 2.4 and 1.6, resolution, respectively. Crystals of selenomethionine-labeled proteins in both crystal forms were obtained by cross-microseeding using the native microcrystals. The structure determination of RfaH and its complex with DNA is in progress. [source]

Cover Picture: A Fusion of Disciplines: Chemical Approaches to Exploit Fusion Proteins for Functional Genomics (ChemBioChem 9/2003)

CHEMBIOCHEM, Issue 9 2003
Nils Johnsson
Abstract The cover picture shows a living cell inside which a protein is labeled with fluorescein. The labeling is based on the unusual mechanism of the DNA repair protein O6 -alkylguanine-DNA alkyltransferase (AGT, structure on the right), which irreversibly transfers the alkyl group from O6 -alkylguanine to its reactive cysteine residue. By using O6 -benzylguanine derivatives such as the fluorescein derivative shown, AGT fusion proteins can be covalently labeled in vivo. The method is one example of a growing number of approaches that aim at equipping proteins with functionalities that can not be genetically encoded, which opens up new ways to study proteins in vivo. Further information can be found in the article by N. Johnsson and K. Johnsson on p. 803,ff. [source]

Marginal zone B cell enrichment and strong follicular B cell reduction correlate with a delayed IgG response in a light chain diversity restricted mouse model

Abstract Recently developed B6.,,,SEG mice (by crossing ,, and C57BL/6 mice congenic for the wild Mus spretus SEG strain , locus lacking genes coding for ,1 and ,3) have a very reduced light chain diversity. B6.,,,SEG mice produce only ,2 and ,x light chains. Regardless of their Igh haplotype, B6.,,,SEG mice show a restricted B cell distribution by light chain subtype with ,x dominance in all peripheral compartments except peritoneal cavity where ,2 is dominant. This distribution suggests that selection mechanisms act differently in different B cell compartments on ,2 and ,x bearing B cells. Sequence analysis before or following immunization did not reveal unusual mechanisms of diversification. B6.,,,SEG mice still respond to various challenging antigens using new Ab patterns. In particular, regardless of Igha or Ighb haplotypes, the anti-2,4-dinitrophenyl response is characterized by a restricted diversity for both heavy and light chains and a delayed IgG response when compared to B6 and B6.,, mice. We suggest that the delayed IgG response is due to the expansion of marginal zone B cells whereas follicular B cells are strongly reduced. [source]