Protein splicing is a unique post-translational process in which an intein excises itself from a precursor with the concomitant ligation of flanking sequences. The binding of zinc to intein inhibits protein splicing reversibly and EDTA relieves the inhibition. Copper was found to inhibit protein trans splicing; however, the recovery of intein splicing required both EDTA and TCEP, suggesting a different inhibition mechanism for copper compared to zinc. In this work, we have investigated the binding properties and inhibition effects of copper ions on the RecA intein from Mycobacterium tuberculosis. Both Cu(+) and Cu(2+) exhibited high binding affinity to inteins, while different binding sites were identified. Cu(2+) coordinates to Cys1, the key residue involved in the mechanism of protein splicing, however, Cu(+) does not coordinate to cysteine. An in vitro inhibition assay indicated that monovalent Cu(+) demonstrates reversible inhibition to protein splicing, and the inhibitory efficiency is comparable to Zn(2+). Redox reaction between Cu(2+) and cysteine in inteins were observed and the rate constants were determined. The results suggested a dual role for Cu(2+) in the inhibition of intein splicing: strong coordination of Cu(2+) to key residues (including Cys1) in the intein, and subsequent oxidation of Cys1, the residue required for the N-->S acyl shift step in protein splicing. A kinetic study suggested that the coordination could be the major cause of inhibition effect of Cu(2+) initially, whereas the redox reaction could play an additional role in inhibition at a later stage.
Multiple coordination modes are present in the Cu II-histidine complex in solution and the copper coordination environment varies with pH. In this work, we have investigated the coordination geometry of Cu(His) 2 complex using X-ray absorption fine structure (XAFS) analysis. Copper K-edge XAFS spectra were acquired on aqueous Cu 2+ samples with histidine at different pH values. The coordination environments were further confirmed by chemically modified histidine. Results show that the caboxylate groups coordinate at acidic condition, while amino and imidazole nitrogens get coordinated at higher pH. For the coordination geometry of Cu(His) 2 in solution at physiological pH, the sixfold coordination is preferentially formed, while the fivefold coordination can co-exist in equilibrium.
Abstract. In this paper, to study the applicability of thermoacoustic detection of composite materials, the distribution of thermoacoustic waves was numerically calculated when there was a nickel domain inside the silicon domain by applying a sinusoidally varying heat source on the surface of solid silicon domain. By changing the width, thickness and position of the internal nickel domain, the applicable conditions of detecting whether there is another material inside the silicon domain by the distribution of the thermoacoustic waves were studied. In addition, a method of judging the width of the inner nickel domain was given. And the corresponding error was studied.
This paper proposed a relay sharing and soft frequency reuse based (RSSFR) frequency planning scheme, which reaches high data rates while using the precious frequency resource efficiently, system performance is analysed and evaluated as well. System performance is enhanced in four aspects: 1) Co-channel interference is reduced significantly, which broadens the area of high achievable data rates in each cell. 2) Base stations (BSs) communicate with fixed relay stations through narrow beam antennas, which boosts the resource efficiency without bringing much interference to mobile stations (MSs). 3) The relay sharing strategy can not only bring down network cost, but also provide a better coverage to cell edge users. 4) Soft frequency reuse on shared relay increases the frequency resource efficiency further. Simulation results show that, a better tradeoff between cell throughput and frequency resource efficiency is achieved in RSSFR.
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