Further investigation of simian immunodeficiency virus Vif function in human cells

Primate lentivirus Vif proteins function by suppressing the antiviral activity of the cell-encoded apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like (APOBEC) proteins APOBEC3G and APOBEC3F. It has been hypothesized that species-specific susceptibilities of APOBEC proteins to Vif proteins may help govern the transmission of primate lentiviruses to new host species. Consistent with this view and with previous results, we report that the Vif proteins of several diverse simian immunodeficiency viruses (SIVs) that are not known to infect humans are not effective inhibitors of human APOBEC3G or APOBEC3F when assessed in transient-transfection experiments. Unexpectedly, this lack of SIV Vif function did not prevent the replication of two vif-deficient SIVs (SIVtan and SIVmnd1; isolated from tantalus monkeys and mandrills, respectively) in a human T-cell line, HUT78, that expresses both APOBEC 3G and APOBEC3F, a finding which demonstrates that some SIVs are partially resistant to the antiretroviral effects of these enzymes irrespective of Vif function. Additional virus replication studies also revealed that the Vif protein of SIVtan is, in fact, active in human T cells, as it substantially enhanced the replication of its cognate virus and human immunodeficiency virus type 1. In sum, we now consider it improbable that species-specific restrictions to SIV Vif function can explain the lack of human infection with certain SIVs. Instead, our data reveal that the species-specific modulation of Vif function is more complex than previously envisioned and that additional (as-yet-unidentified) viral or host factors may be involved in regulating this dynamic interaction between host and pathogen.     

Effect of Enhanced UV-B Radiation on Polyamine Content and Membrane Permeability in Cucumber Leaves

Cucumber plants (Cucumis sativus L., cv. Jingchun 3) were grown in a greenhouse under PAR illumination of 400–600 mol/(m² s) at 30/15°C (day/night) temperature. Two enhanced biologically effective UV-B radiation levels per day were applied: 8.82 kJ/m² (T₁) and 12.6 kJ/m² (T₂). Cucumber seedlings were irradiated 7 h per day for 25 days under T₁ and T₂. A comparative study of growth, membrane permeability, and polyamine content in cucumber leaves under T₁ and T₂ treatments was conducted. UV-B radiation resulted in the dose-dependent decrease in leaf area, dry weight of foliage, and plant height. The T₁ and T₂ treatments caused an increase in the contents of putrescine, spermine, and spermidine. However, the total polyamine content declined slightly when electrolyte leakage increased dramatically on the 18th day of treatment, especially after T₂ treatment. It can be concluded that polyamine accumulation in the cucumber leaves is an adaptive mechanism to the stress caused by UV-B radiation.     

天鹅洲故道水生态研究进展

20世纪90年代初, 湖北长江天鹅洲故道水质良好, 鱼类资源丰富, 被认为是建立长江豚类半自然保护区和四大家鱼种质资源生态库的理想场所, 而对之开展了水生态研究, 之后由于成功实现了长江江豚的迁地保护而受到越来越多的关注。学者们从水质和沉积物等环境因素, 浮游植物、浮游动物、底栖动物和高等水生植物等生物因素, 水体初级生产力、渔产潜力和鱼类等资源因素多角度开展了天鹅洲故道水生态研究。天鹅洲故道水质呈恶化趋势。浮游植物数量增加了2个数量级, 且从单细胞个体转变为多细胞群体, 同时带有胶被的蓝藻在种类和密度上占有绝对优势; 浮游动物优势种呈小型化趋势; 底栖动物密度有所下降; 高等水生植物呈逐渐衰退趋势。鱼类资源量呈下降趋势。根据水质化学和生物学评价结果, 结合天鹅洲故道受人类活动的影响, 本文指出故道与长江阻隔、渔业活动和环境污染是天鹅洲故道水生态面临的主要问题, 其通过水质、饵料和栖息地等方面影响长江江豚的可持续性生存。同时, 提出5个方面的建议: 首先, 实施通江工程, 恢复故道水文特征, 提高故道理化环境异质性; 其次, 控制外源和内源营养负荷, 提高故道水体水质; 然后, 持续监测水质、沉积物和水生生物状况, 建立故道水生态数据库; 再次, 实施生态修复工程, 提高水生生物多样性; 最后, 规范渔业活动, 优化故道渔业资源, 为保护天鹅洲故道水环境质量和水生态健康, 维持江豚可持续生存提供依据。     

Study of the physiological mechanisms of two species of <Emphasis Type="Italic">Spiraea</Emphasis> during adaptation to drought treatment

The photosynthetic rate, light saturation point, light compensation point, changes in the MDA and SOD activities, and protein expression of two different drought-resistance species, Spiraea fritschiana and Spiraea trichocarpa, were assessed in this study. Furthermore, the drought-resistant physiological mechanisms of both species were analyzed at the protein level. The photosynthetic capacities of two Spiraea species decreased under drought stress, and the light saturation point and light compensation point decreased. However, their capacities to use weak light increased. Spiraea fritschiana, which demonstrated a stronger drought resistance, showed a better ability to adapt to weak light than S. trichocarpa. The content of MDA in S. fritschiana was notably lower than that in S. trichocarpa, indicating that the concentration of the membrane peroxidation products of S. fritschiana was less than those of S. trichocarpa. Compared with S. trichocarpa, S. fritschiana’s SOD activity was higher, and its ability to remove ROS was also better. Sixty-six proteins were identified with significantly different expression behavior and included regulatory, redox homeostasis, metabolism and energy, and cytoskeleton proteins. The results showed that the photosynthesis of S. trichocarpa was significantly affected by the drought stress. Enzymes in photosynthesis changed significantly; the expression of the RuBisCo large subunit decreased; and RuBisCo carboxylase, the chlorophyll a–b binding protein, ATP synthase, OEC 33 kD photosystem II protein and 23 kD OEC protein greatly increased. In addition, four antioxidant enzymes greatly increased, GroES chaperonin decreased, and eIF5A significantly increased under light stress. When S. fritschiana Schneid encountered serious drought stress, in addition to those enzymes that changed significantly under light drought stress in S. trichocarpa Nakai, NAD(P)H-quinone oxidoreductase and eIF5A were up-regulated. Specifically, three heat-shock proteins were induced. The expression of the enzymes of the two Spiraea that were related to photosynthesis, oxidation–reduction and regulation were all affected, but their species and expression patterns were different. In S. trichocarpa Nakai and S. fritschiana Schneid, there were significant changes in the proteins related to energy metabolism and the proteins related to energy transport, respectively. Thus, we considered that, in the case of protein involvement, the differences in the metabolic pathways and adjustment levels might contribute to S. trichocarpa having a weaker drought tolerance than S. fritschiana.     

A Shinella β-N-acetylglucosaminidase of glycoside hydrolase family 20 displays novel biochemical and molecular characteristics

β-N-Acetylglucosaminidases (GlcNAcases) are important for many biological functions and industrial applications. In this study, a glycoside hydrolase family 20 GlcNAcase from Shinella sp. JB10 was expressed in Escherichia coli BL21 (DE3). Compared to many GlcNAcases, the purified recombinant enzyme (rJB10Nag) exhibited a higher specificity activity (538.8 µmol min⁻¹ mg⁻¹) or V _max (1030.0 ± 82.1 µmol min⁻¹ mg⁻¹) toward p-nitrophenyl β-N-acetylglucosaminide and N,N′-diacetylchitobiose (specificity activity of 35.4 µmol min⁻¹ mg⁻¹) and a higher N-acetylglucosaminide tolerance (approximately 50% activity in 70.0 mM N-acetylglucosaminide). The degree of synergy on enzymatic degradation of chitin by a commercial chitinase and rJB10Nag was as high as 2.35. The enzyme was tolerant to most salts, especially 3.0–15.0% (w/v) NaCl and KCl. These biochemical characteristics make the JB10 GlcNAcase a candidate for use in many potential applications, including processing marine materials and the bioconversion of chitin waste. Furthermore, the enzyme has the highest proportions of alanine (16.5%), glycine (10.5%), and random coils (48.8%) with the lowest proportion of α-helices (24.9%) among experimentally characterized GH 20 GlcNAcases from other organisms.

     

The Par-3 NTD adopts a PB1-like structure required for Par-3 oligomerization and membrane localization

The evolutionarily conserved Par-3/Par-6/aPKC complex is essential for the establishment and maintenance of polarity of a wide range of cells. Both Par-3 and Par-6 are PDZ domain containing scaffold proteins capable of binding to polarity regulatory proteins. In addition to three PDZ domains, Par-3 also contains a conserved N-terminal oligomerization domain (NTD) that is essential for proper subapical membrane localization and consequently the functions of Par-3. The molecular basis of NTD-mediated Par-3 membrane localization is poorly understood. Here, we describe the structure of a monomeric form of the Par-3 NTD. Unexpectedly, the domain adopts a PB1-like fold with both type-I and type-II structural features. The Par-3 NTD oligomerizes into helical filaments via front-to-back interactions. We further demonstrate that the NTD-mediated membrane localization of Par-3 in MDCK cells is solely attributed to its oligomerization capacity. The data presented in this study suggest that the Par-3 NTD is likely to facilitate the assembly of higher-order Par-3/Par-6/aPKC complex with increased avidities in targeting the complex to the subapical membrane domain and in binding to other polarity-regulating proteins.     

Peripheral disruption of the Grb10 gene enhances insulin signaling and sensitivity in vivo

Grb10 is a pleckstrin homology and Src homology 2 domain-containing protein that interacts with a number of phosphorylated receptor tyrosine kinases, including the insulin receptor. In mice, Grb10 gene expression is imprinted with maternal expression in all tissues except the brain. While the interaction between Grb10 and the insulin receptor has been extensively investigated in cultured cells, whether this adaptor protein plays a positive or negative role in insulin signaling and action remains controversial. In order to investigate the in vivo role of Grb10 in insulin signaling and action in the periphery, we generated Grb10 knockout mice by the gene trap technique and analyzed mice with maternal inheritance of the knockout allele. Disruption of Grb10 gene expression in peripheral tissues had no significant effect on fasting glucose and insulin levels. On the other hand, peripheral-tissue-specific knockout of Grb10 led to significant overgrowth of the mice, consistent with a role for endogenous Grb10 as a growth suppressor. Loss of Grb10 expression in insulin target tissues, such as skeletal muscle and fat, resulted in enhanced insulin-stimulated Akt and mitogen-activated protein kinase phosphorylation. Hyperinsulinemic-euglycemic clamp studies revealed that disruption of Grb10 gene expression in peripheral tissues led to increased insulin sensitivity. Taken together, our results provide strong evidence that Grb10 is a negative regulator of insulin signaling and action in vivo.