Analysis of FtsZ assembly by light scattering and determination of the role of divalent metal cations

FtsZ is an ancestral homologue of tubulin that polymerizes in a GTP-dependent manner. In this study, we used 90 degrees angle light scattering to investigate FtsZ polymerization. The critical concentration for polymerization obtained by this method is similar to that obtained by centrifugation, confirming that the light scattering is proportional to polymer mass. Furthermore, the dynamics of FtsZ polymerization could be readily monitored by light scattering. Polymerization was very rapid, reaching steady state within 30 s. The length of the steady-state phase was proportional to the GTP concentration and was followed by a rapid decrease in light scattering. This decrease indicated net depolymerization that always occurred as the GTP in the reaction was consumed. FtsZ polymerization was observed over the pH range 6.5 to 7.9. Importantly, Mg2+ was not required for polymerization although it was required for the dynamic behavior of the polymers. It was reported that 7 to 25 mM Ca2+ mediated dynamic assembly of FtsZ (X. -C. Yu and W. Margolin, EMBO J. 16:5455-5463, 1997). However, we found that Ca2+ was not required for FtsZ assembly and that this concentration of Ca2+ reduced the dynamic behavior of FtsZ assembly.     

Protein-resistant coatings for glass and metal oxide surfaces derived from oligo(ethylene glycol)-terminated alkytrichlorosilanes

This paper describes the preparation of oligo(ethylene glycol)-terminated alkyltrichlorosilanes, Cl3Si(CH2)11(OCH2CH2)(n)OCH3 (n = 2, 3), and their use in the formation of self-assembled monolayers on an oxide surface. The adsorption of the trichlorosilanes from solution produces densely packed, oriented monolayer films that are 2-3 nm in thickness. The trichlorosilyl group anchors the molecules to the surface, and the resulting film exposes the ethylene glycol units at its surface, as noted by its moderate hydrophilicity (theta2(H2O) approximately 68 degrees). The films are robust with stabilities similar to those of other alkylsiloxane coatings. These oligo(ethylene glycol)-terminated silane reagents produce films that notably exhibit resistances against the non-specific adsorption of proteins from solution that are better than for films prepared from octadecyltrichlorosilane. With insulin, tysozyme, albumin, and hexokinase, no adsorption was observed with the oligo(ethylene glycol)-siloxane coatings whereas protein films of approximately a monolayer formed on surfaces-treated with octadecyltrichlorosilane. With fibrinogen, complete resistance was not possible with either coating; however, the oligo(ethylene glycol)-siloxane coatings exhibited greater resistance against non-specific adsorption. The oligo(ethylene glycol)-siloxane coatings offer performance advantages over available systems and could easily provide a direct and superior replacement in protocols that presently use silane reagents to generate hydrophobic, 'inert' surfaces.     

二维过渡金属碳化物/碳氮化物（MXene）的稳定性及改进方法

二维（2D）过渡金属碳化物/碳氮化物(Mxene)材料,因其良好的亲水性、导电性、柔韧性以及高赝电容等特性,在储能、海水淡化、催化、电磁干扰屏蔽、透明导电薄膜等领域有着巨大的应用潜力。然而,由于MXene材料中活性过渡金属、表面官能团以及结构缺陷的存在,使其在无保护的环境中（含有水、氧等）很容易被氧化,导致稳定性较差。MXene材料的氧化破坏了其片状结构,降低了其电导率,限制了其更广泛的应用。本文简要介绍了MXene的结构和合成方法;综述了MXene在不同条件下不稳定的机理,即表面官能团和周围介质发生氧化反应;并从储存条件、合成方法、气氛热处理、表面电性修饰、掺杂等方面讨论了提高MXene稳定性的方法。      

Endothelin ET(B) receptors counteract venoconstrictor effects of endothelin-1 in anesthetized rats

The inhibitory effects of BQ 788 (3 mg/kg, i.v., ET(B)-receptor antagonist) on endothelin-1 (ET-1)- or IRL 1620 (ET(B)-receptor agonist)-induced changes in mean arterial pressure (MAP), mean circulatory filling pressure (MCFP, driving force of venous return), arterial resistance (RA), venous resistance (RV) and cardiac output (CO) were characterized in 6 groups of pentobarbital-anesthetized rats. ET-1 or IRL 1620 (0.5, 1 and 2 nmol/kg, i.v.) dose-dependently increased MAP, RA, RV and MCFP and decreased CO. Maximum changes in RA, RV and CO elicited by ET-1 were greater than those by IRL 1620. Equimolar doses of ET-1 and IRL 1620 also caused similar initial transient decreases in MAP. BQ 788 alone slightly elevated MCFP, but did not alter other variables. The ET(B)-blocker abolished all changes elicited by IRL 1620, but only partially inhibited its responses on MCFP, showing the presence of BQ 788-insensitive receptors. BQ 788 also abolished ET-1's depressor response, partially inhibited its effect on MCFP, and markedly augmented its effects on RA, RV and CO. Thus, ET(B)-receptors counteract the sustained constrictor effects of ET-1 on arterial and venous resistance vessels Our results indicate a substantial arterial and venous dilator role for ET(B) receptors.     

Multi-objective optimization of gas metal arc welding parameters and sequences for low-carbon steel (Q345D) T-joints

Q345D high-quality low-carbon steel has been extensively employed in structures with stringent weld-ing quality requirements.A multi-objective optimization of welding stress and deformation was presented to design reasonable values of gas metal arc welding parameters and sequences of Q345D T-joints.The optimized factors included continuous variables (welding current (I), welding voltage (U) and welding speed (v)) and discrete variables (welding sequence (S) and welding direc-tion (D)).The concepts of the pointer and stack in Visual Basic (VB) and the interpolation method were introduced to optimize the variables.The optimization obj ectives included the different combina-tions of the angular distortion and transverse welding stress along the transverse and longitudinal dis-tributions.Based on the design of experiments (DOE) and the polynomial regression (PR) model, the finite element (FE) results of the T-joint were used to establish the mathematical models.The Pareto front and the compromise solutions were obtained by using a multi-objective particle swarm optimization (MOPSO) algorithm.The optimal results were validated by the corresponding results of the FE method, and the error between the FE results and the two-objective results as well as that be-tween the FE results and the three-objective optimization results were less than 17.2% and 21.5%, respectively.The influence and setting regularity of different factors were discussed according to the compromise solutions.     

Effect of flanking sequences on the right- to left-handed transition of a (dA-dT)n tract in supercoiled DNA

Alternating (dA-dT)n sequences in supercoiled DNA may undergo a transition to a left-handed conformation in the presence of Ni2+ ions and high NaCl concentration (Nejedly, K., Klysik, J. and Palecek, E., FEBS Lett. 243, 313-317 (1989)). In this work we have found that ionic conditions necessary for the B-to-Z transition are strongly dependent on the sequences flanking the (dA-dT)n tract. In particular, the presence of 5'-homopyrimidine (C3) and 3'-homopurine (G4) blocks adjacent to the tract were found to facilitate the transition to the left-handed form. Within a constant sequence context it was found that the ionic strength required to promote the transition was inversely proportional to the length of the (dA-dT)n sequence.     

Analysis of the mechanism of lipoprotein(a) assembly

We have assessed the ability of a battery of purified recombinant apolipoprotein(a) (r-apo(a)) derivatives to bind to immobilized low-density lipoprotein (LDL) by ELISA. Removal of the apo(a) kringle IV type 8 and type 9 sequences dramatically reduced apo(a) binding to LDL. The binding of apo(a) to LDL was effectively inhibited by arginine, lysine, the lysine analogue epsilon-aminocaproic acid and proline; comparable inhibition was observed using the 17K and KIV5-8 r-apo(a) derivatives, suggesting a direct role for sequences contained in the latter species in mediating the initial non-covalent interactions which precede specific disulfide bond formation. We also determined that r-apo(a) binds directly to a synthetic apoB peptide spanning amino acid residues 3732-3745; this interaction appeared to be mediated by sequences present in apo(a) kringle IV types 8 and 9, and could be inhibited by arginine, lysine and proline. The results of this study indicate that the efficiency of Lp(a) assembly is a direct function of the initial non-covalent interactions between apo(a) and LDL; in addition, these studies suggest that Cys3734 in apoB mediates covalent linkage with apo(a) by virtue of the ability of the apoB sequences surrounding this residue to directly interact with apo(a) KIV type 9.     

Stereodifferentiation--the effect of P chirality of oligo(nucleoside phosphorothioates) on the activity of bacterial RNase H

P stereoregular phosphorothioate analogs of pentadecamer 5'-d(AGATGTTTGAGCTCT)-3' were synthesized by the oxathiaphospholane method. Their diastereomeric purity was assigned by means of enzymatic degradation with nuclease P1 and, independently, with snake venom phosphodiesterase. DNA-RNA hybrids formed by phosphorothioate oligonucleotides (PS-oligos) with the corresponding complementary pentadecaribonucleotide were treated with bacterial RNase H. The DNA-RNA complex containing the PS-oligo of [all-RP] configuration was found to be more susceptible to RNase H-dependent degradation of the pentadecaribonucleotide compared with hybrids containing either the [all-SP] counterpart or the so called 'random mixture of diastereomers' of the pentadeca(nucleoside phosphorothioate). This stereodependence of RNase H action was also observed for a polyribonucleotide (475 nt) hybridized with these phosphorothioate oligonucleotides. The results of melting studies of PS-oligo-RNA hybrids allowed a rationalization of the observed stereodifferentiation in terms of the higher stability of heterodimers formed between oligoribonucleotides and [all-RP]-oligo(nucleoside phosphorothioates), compared with the less stable heterodimers formed with [all-SP]-oligo(nucleoside phosphorothioates) or the random mixture of diastereomers.     

Acid-facilitated supramolecular assembly of G-quadruplexes in d(CGG)4

Molar [K+] induces aggregate formation in d(CGG)4, as evidenced by absorbance, circular dichroic (CD), and gel measurements. The kinetics of this transformation are extremely slow at pH 8 but are found to be greatly facilitated in acidic conditions. Kinetic profiles via absorbance or CD monitoring at single wavelength resemble those of autocatalytic reacting systems with characteristic induction periods. More than 0.8 M KCl is needed to observe the onset of aggregation at 20 degrees C and pH 5.4 within the time span of 1 day. Time-dependent CD spectral characteristics indicate the formation of parallel G-tetraplexes prior to the onset of aggregation. Despite the evidence of K(+)-induced parallel G-quadruplex and higher molecular weight complex formation, both d(TGG)4 and d(CGG)4T fail to exhibit the observed phenomenon, thus strongly implicating the crucial roles played by the terminal G and base protonation of cytosines. A plausible mechanism for the formation of a novel self-assembled structure is speculated. Aided by the C+.C base pair formation, parallel quadruplexes are initially formed and subsequently converted to quadruplexes with contiguous G-tetrads and looped-out cytosines due to high [K+]. These quadruplexes then vertically stack as well as horizontally expand via interquadruplex C+.C base pairing to result in dendrimer-type self-assembled super structures.     

Solution conformation of the N-(deoxyguanosin-8-yl)-1-aminopyrene ([AP]dG) adduct opposite dC in a DNA duplex

Combined NMR-molecular mechanics computational studies were undertaken on the C8-deoxyguanosine adduct formed by the carcinogen 1-nitropyrene embedded in the d(C5-[AP]G6-C7).d(G16-C17-G18) sequence context in a 11-mer duplex, with dC opposite the modified deoxyguanosine. The exchangeable and nonexchangeable protons of the aminopyrene moiety and the nucleic acid were assigned following analysis of two-dimensional NMR data sets in H2O and D2O solution. There was a general broadening of several proton resonances for the three nucleotide d(G16-C17-G18) segment positioned opposite the [AP]dG6 lesion site resulting in weaker NOEs involving these protons in the adduct duplex. The solution conformation of the [AP]dG.dC 11-mer duplex has been determined by incorporating intramolecular and intermolecular proton-proton distances defined by upper and lower bounds deduced from NOESY spectra as restraints in molecular mechanics computations in torsion angle space. The aminopyrene ring of [AP]dG6 is intercalated into the DNA helix between intact Watson-Crick dC5.dG18 and dC7.dG16 base pairs. The modified deoxyguanosine ring of [AP]dG6 is displaced into the major groove and stacks with the major groove edge of dC5 in the adduct duplex. Both carbon and proton chemical shift data for the sugar resonances of the modified deoxyguanosine residue are consistent with a syn glycosidic torsion angle for the [AP]dG6 residue. The dC17 base on the partner strand is displaced from the center of the helix toward the major groove as a consequence of the aminopyrene ring intercalation into the helix. This base-displaced intercalative structure of the [AP]dG.dC 11-mer duplex exhibits several unusually shifted proton resonances which can be accounted for by the ring current contributions of the deoxyguanosinyl and pyrenyl rings of the [AP]dG6 adduct. In summary, intercalation of the aminopyrene moiety is accompanied by displacement of both [AP]dG6 and the partner dC17 into the major groove in the [AP]dG.dC 11-mer duplex.     

金属消费量与其折旧再生指数之间的关系(I)

根据统计资料,将金属消费函数总结为4类基本特征和由基本特征组合成的4种组合特征.分析了金属消费函数表现为基本特征时与其折旧再生指数的变化关系.根据金属折旧再生指数的变化情况,可以分析金属工业中金属折旧再生资源的充足程度.