Solution structure of inhibitor-free human metalloelastase (MMP-12) indicates an internal conformational adjustment

Macrophage metalloelastase or matrix metalloproteinase-12 (MMP-12) appears to exacerbate atherosclerosis, emphysema, aortic aneurysm, rheumatoid arthritis, and inflammatory bowel disease. An inactivating E219A mutation, validated by crystallography and NMR spectra, prevents autolysis of MMP-12 and allows us to determine its NMR structure without an inhibitor. The structural ensemble of the catalytic domain without an inhibitor is based on 2813 nuclear Overhauser effects (NOEs) and has an average RMSD to the mean structure of 0.25 Å for the backbone and 0.61 Å for all heavy atoms for residues Trp109-Gly263. Compared to crystal structures of MMP-12, helix B (hB) at the active site is unexpectedly more deeply recessed under the β-sheet. This opens a pocket between hB and β-strand IV in the active-site cleft. Both hB and an internal cavity are shifted toward β-strand I, β-strand III, and helix A on the back side of the protease. About 25 internal NOE contacts distinguish the inhibitor-free solution structure and indicate hB's greater depth and proximity to the sheet and helix A. Line broadening and multiplicity of amide proton NMR peaks from hB are consistent with hB undergoing a slow conformational exchange among subtly different environments. Inhibitor-binding-induced perturbations of the NMR spectra of MMP-1 and MMP-3 map to similar locations across MMP-12 and encompass the internal conformational adjustments. Evolutionary trace analysis suggests a functionally important network of residues that encompasses most of the locations adjusting in conformation, including 18 residues with NOE contacts unique to inhibitor-free MMP-12. The conformational change, sequence analysis, and inhibitor perturbations of NMR spectra agree on the network they identify between structural scaffold and the active site of MMPs.     

Effects of Precommercial Thinning on Snowshoe Hares in Maine

Abstract: Snowshoe hares (Lepus americanus) are an important prey species and a dominant herbivore across much of their North American range, and researchers have questioned the influences of forestry practices that alter habitat for hares and the potential community-level effects on carnivores. We examined the effects of precommercial thinning (PCT) from 1 to 11 years posttreatment on snowshoe hares. In the commercial forests of northern Maine, USA, we counted and cleared hare pellets twice a year during 2001 and 2002 on >46 km of pellet transects across 30 regenerating conifer stands (17 treated with PCT) previously treated with an aerial application of herbicide. We compared densities of snowshoe hare pellets among 3 development classes with (1 yr after thinning, 6 yr after thinning, and 11 yr after thinning) and without thinning (stands with a similar history of clearcut and herbicide treatment but no thinning). During both years, densities of hares were lower in stands treated with PCT than in similar unthinned stands across the 3 development classes and during both leaf-off and leaf-on seasons (P < 0.001). Within both thinned and unthinned stands, hare density was greatest in stands in the 1-year development class when compared to the 6-year and 11-year development classes, but a statistical difference (P = 0.048) among classes was evident only during leaf-off seasons. Precommercial thinning was associated with densities of snowshoe hares that were approximately half of those in similar unthinned stands up to at least 11 years posttreatment; however, thinned stands may retain densities of hares greater than stands managed using other forest harvesting regimes. Our results apply to core portions of stands with crop trees spaced at 1.8–2.4-m intervals following complete overstory removal and herbicide treatment. We advocate caution when applying our results to other thinning regimes or across broader spatial scales.     

Electromagnetic fields produced by GSM cellular phones and heart rate variability

In this study, 26 healthy young volunteers were submitted to 900 MHz (2 W) GSM cellular phone exposure and to sham exposure in separate sessions. The study was designed to assess cardiac regulatory mechanism in different autonomic nervous system (ANS) states during exposure to low-intensity EMF. Rest-to-stand protocol was applied to evaluate ANS in quiet condition (rest, vagal prevalence) and after a sympathetic activation (stand). The procedure is conducted twice in a double-blind design: once with a genuine EMF exposure and once with a sham exposure (at least 24 h apart). During each session three-leads electrocardiograms were recorded and RR series extracted off-line. Time domain and frequency domain HRV parameters were calculated in every phase of the protocol and during different exposures. The analysis of the data show there was no statistically significant effect due to EMF exposure both on main (i.e., RR mean) and most of the other HRV parameters. A weak interaction between some HRV parameters (i.e., SDNN, TINN, and triangular index in time domain and LF power in frequency domain analysis) and RF exposure was observed and this effect seems to be gathered around the sympathetic response to stand.     

Effect of sodium chloride on the response of the halophyte species <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis> grown in mannitol-induced water stress

Sesuvium portulacastrum is a halophytic species well adapted to salinity and drought. In order to evaluate the physiological impact of salt on water deficit-induced stress response, we cultivated seedlings for 12 days, in the presence or absence of 100 mmol l⁻¹ NaCl, on a nutrient solution containing either 0 mmol l⁻¹ or 25 mmol l⁻¹ mannitol. Mannitol-induced water stress reduced growth, increased the root/shoot ratio, and led to a significant decrease in water potential and leaf relative water content, whereas leaf Na⁺ and K⁺ concentrations remained unchanged. The addition of 100 mmol l⁻¹ NaCl to 25 mmol l⁻¹ mannitol-containing medium mitigated the deleterious impact of water stress on growth of S. portulacastrum, improved the relative water content, induced a significant decrease in leaf water potential and, concomitantly, resulted in enhancement of overall plant photosynthetic activity (i.e. CO₂ net assimilation rate, stomatal conductance). Presence of NaCl in the culture medium, together with mannitol, significantly increased the level of Na⁺ and proline in the leaves, but it had no effect on leaf soluble sugar content. These findings suggest that the ability of NaCl to improve plant performance under mannitol-induced water stress may be due to its effect on osmotic adjustment through Na⁺ and proline accumulation, which is coupled with an improvement in photosynthetic activity. A striking recovery in relative water content and growth of the seedlings was also recorded in the presence of NaCl on release of the water stress induced by mannitol.     

Exogenous Glycine Betaine Reduces Drought Damage by Mediating Osmotic Adjustment and Enhancing Antioxidant Defense in <i>Phoebe hunanensis</i>

Drought stress negatively impacts growth and physiological processes in plants. The foliar application of glycine betaine (GB) is an effective and low-cost approach to improve the drought tolerance of trees. This study examined the effect of exogenously applied GB on the cell membrane permeability, osmotic adjustment, and antioxidant enzyme activities of Phoebe hunanensis Hand.-Mazz under drought stress. Two levels (0 and 800 mL) of water irrigation were tested under different applied GB concentrations (0, 50, 100, and 200 mM). Drought stress decreased the relative water content by 58.5% while increased the electric conductivity, malondialdehyde, proline, soluble proteins, soluble sugars, and antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase) by up to 62.9%, 42.4%, 87.0%, 19.1%, 60.5%, 68.3%, 71.7%, and 83.8%, respectively, on the 25^th day. The foliar application of GB, especially at 100 mM, increased the relative water content of P. hunanensis leaves under drought stress. The concentration of GB from 50 to 100 mM effectively alleviated the improvement of cell membrane permeability and inhibited the accumulation of membrane lipid peroxidation products. Under drought stress, the concentrations of proline, soluble proteins, and soluble sugars in the leaves of P. hunanensis increased as the applied GB concentration was increased and the water stress time was prolonged. Exogenously applied GB decreased oxidative stress and improved antioxidant enzyme activities as compared with treatments without GB application. Furthermore, the physiological and biochemical indexes of P. hunanensis showed a certain dose effect on exogenous GB concentration. These results suggest that GB helps maintain the drought tolerance of P. hunanensis.     

樟子松幼树株高及其逆境生理指标对沙埋的响应特征

以3龄樟子松幼树为材料,2013年在科尔沁沙地研究了不同沙埋深度下其株高、叶片膜透性、渗透调节物质含量及保护酶活性变化,以揭示沙埋条件下樟子松幼树生长及其对逆境的生理响应特征。结果显示:(1)在沙埋深度低于株高以上2cm时被埋樟子松幼树能够正常生长,其株高和芽长均明显高于非沙埋对照,并以沙埋深度为株高的50%时增长幅度最大;当沙埋深度超过株高2cm以上时,虽然植株高度和芽长也较埋前有一定增长,但均低于对照,且所有处理植株均未破土,后来全部死亡。(2)所有沙埋处理的叶片可溶性糖含量均显著低于对照,而POD活性显著高于对照,可溶性蛋白质和脯氨酸含量也高于对照。(3)随沙埋深度增加,叶片相对含水量总体呈增加趋势,但大多数处理与对照差异不显著;丙二醛含量基本呈显著下降趋势,可溶性蛋白和脯氨酸含量先增加后下降,而大多数处理的膜透性与对照差异不显著;随着沙埋深度增加,叶片可溶性糖含量显著下降,SOD和POD活性均先增加后下降。(4)相关分析显示,樟子松幼树叶片膜透性变化与MDA含量变化相关性几乎为零,可溶性蛋白与脯氨酸含量呈显著正相关关系,可溶性糖含量与脯氨酸含量呈显著负相关关系。研究表明,沙埋深度低于樟子松株高以上2cm能够促进其幼树生长;沙埋并没有导致樟子松幼树体内的膜脂过氧化,也没有引起细胞膜的损伤,在受到沙埋胁迫时,樟子松幼树体内SOD、POD以及可溶性蛋白和脯氨酸分别在防止其膜脂过氧化和维持细胞膨压中起到重要作用,而可溶性糖含量在沙埋过程中没有起到渗透调节作用。     

Removal of highly elevated nitrate from drinking water by pH-heterogenized heterotrophic denitrification facilitated with ferrous sulfide-based autotrophic denitrification

The performance of acetic acid-supported pH-heterogenized heterotrophic denitrification (HD) facilitated with ferrous sulfide-based autotrophic denitrification (AD) was investigated in upflow activated carbon-packed column reactors for reliable removal of highly elevated nitrate (42 mg NO₃-N l⁻¹) in drinking water. The use of acetic acid as substrate provided sufficient internal carbon dioxide to completely eliminate the need of external pH adjustment for HD, but simultaneously created vertically heterogenized pH varying from 4.8 to 7.8 in the HD reactor. After 5-week acclimation, the HD reactor developed a moderate nitrate removal capacity with about one third of nitrate removal occurring in the acidic zone (pH 4.8–6.2). To increase the treatment reliability, acetic acid-supported HD was operated under 10% carbon limitation to remove >85% of nitrate, and ferrous sulfide-based AD was supplementally operated to remove residual nitrate and formed nitrite without excess of soluble organic carbon, nitrite or sulfate in the final effluent.     

四季竹对不同浓度NaCl胁迫的生理响应

以夏秋季优良笋用竹种四季竹盆栽苗为材料,研究了土壤中1‰~6‰浓度NaCl(干重)处理对四季竹叶片脱落率、离子渗漏率、丙二醛(MDA)含量、抗氧化酶活性以及渗透调节物质含量的变化特征,以探讨四季竹的抗盐机理。结果表明:(1)随NaCl浓度的增大和处理时间的延长,四季竹叶片脱落率逐渐增加;四季竹在1‰~2‰NaCl浓度下的土壤中生长良好,在3‰~5‰浓度下随处理浓度的增大伤害逐渐加重,但这种伤害是可逆的,6‰是四季竹的半致死盐浓度。(2)叶片离子渗漏率随NaCl浓度的增大而显著增大,在6‰浓度处理下随处理时间的延长近直线升高,在3‰~5‰浓度下先升高后降低,而在1‰~2‰浓度处理下变化平缓且与同期对照无显著差异;叶片MDA含量随NaCl浓度的增大而增加,随处理时间的延长先增加后降低。(3)四季竹叶片SOD和POD活性在胁迫3~15 d均出现先下降后上升的过程,其有一定的锻炼适应性;叶片脯氨酸含量随NaCl处理浓度的增大而增加,其随处理时间的延长在1‰~2‰浓度处理下变化平缓,在3‰~6‰浓度处理下显著增加后减小;各浓度处理的可溶性蛋白含量随处理时间的延长先增加后减小,但均高于对照。研究发现,四季竹是较耐盐竹种,其可以通过调控自身保护酶活性和渗透调节物质含量来有效缓解盐胁迫伤害,从而表现出一定的耐盐能力。     

万寿菊属不同品种初花期抗旱特性分析

以万寿菊属(Tagetes)9个品种为试验材料,研究了自然持续干旱胁迫对它们初花期的花最大直径、叶色、旱害指数等形态指标以及叶绿素含量(Chl a+b,Ch a/b)、叶片相对含水量(RWC)、叶片保水力(WHC)、叶片和花的脯氨酸、可溶性糖和可溶性蛋白含量等生理指标的影响,以揭示其抗旱特性及其生理机制.结果显示:(1)持续6d干旱胁迫条件下,万寿菊9个品种花的最大直径显著降低,叶绿素含量和相对含水量均呈明显下降趋势.(2)万寿菊叶片的脯氨酸、可溶性蛋白和可溶性糖含量均呈上升趋势;而花的脯氨酸含量持续上升,可溶性蛋白含量呈下降趋势,但可溶性糖含量变化趋势复杂.(3)万寿菊旱害指数与其叶片相对含水量、叶绿素总含量、叶片和花的脯氨酸含量、叶片可溶性蛋白含量呈极显著相关.研究表明,抗旱性强的品种可以通过调节自身的渗透调节物质含量减轻干旱伤害;9个品种初花期抗旱性强弱依次为:珍妮>金门>鸿运>拳王>巨人>发现>小英雄>大英雄>迪阿哥.