两端融合表达几丁质结合结构域提高几丁质酶抗真菌活性

【目的】通过两端融合表达几丁质结合结构域来提高几丁质酶的活性和生物防治植物病原真菌能力。【方法】以苜蓿链霉菌(Streptomyces alfalae)ACCC40021中唯一的GH19家族几丁质酶为模板,构建两端融合表达几丁质结合结构域的几丁质酶,并进行原核表达;利用3,5-二硝基水杨酸法(DNS)测定几丁质酶活。【结果】成功构建了CatD_(ChiB) (催化结构域)、rChiB (含N-端几丁质结合结构域)、DChBD_(ChiB)(含两端几丁质结合结构域)三种形式的酶,并在大肠杆菌中得到了高效表达;与CatD_(ChiB)和rChiB相比,DChBD_(ChiB)显著地提高了对α-几丁质、胶体几丁质和黑曲霉几丁质的结合能力和活性;同时增强了其对病原真菌长枝木霉的抑制作用。【结论】两端融合表达几丁质结合结构域是简单有效的提高几丁质酶活性及抗真菌活性的策略。     

Evaporation‐Free Nonfullerene Flexible Organic Solar Cell Modules Manufactured by An All‐Solution Process

To ensure laboratory‐to‐industry transfer of next‐generation energy harvesting organic solar cells (OSCs), it is necessary to develop flexible OSC modules that can be produced on a continuous roll‐to‐roll basis and to apply an all‐solution process. In this study, nonfullerene acceptors (NFAs)‐based donor polymer, SMD2, is newly designed and synthesized to continuously fabricate high‐performance flexible OSC modules. Also, multifunctional hole transport layers (HTLs), WO₃/HTL solar bilayer HTLs, are developed and applied via an all‐solution process called “ProcessOne” into inverted structure. SMD2, the donor terpolymer, has a deep highest occupied molecular orbital (HOMO) level and can achieve a power conversion efficiency (PCE) of 11.3% with NFAs without any pre‐/post‐treatment because of its optimal balance between crystallinity and miscibility. Furthermore, the integration of multifunctional HTLs enables the recovery of the drop in open circuit voltage (V_OC) caused by a mismatch in energy levels between the deep HOMO level of the NFAs‐based bulk‐heterojunction layer and the solution‐processed HTLs. Also, the photostability under ultraviolet‐exposure necessary for “ProcessOne” is greatly improved because of the integration of multifunctional HTLs. Consequently, because of the synergistic effects of these approaches, the flexible OSC modules fabricated in an industrial production line have a PCE of 5.25% (P_max = 419.6 mW) on an active area of 80 cm².     

Exploring Multimodularity in Plant Cell Wall Deconstruction: STRUCTURAL AND FUNCTIONAL ANALYSIS OF Xyn10C CONTAINING THE CBM22-1–CBM22-2 TANDEM*

Elucidating the molecular mechanisms regulating multimodularity is a challenging task. Paenibacillus barcinonensis Xyn10C is a 120-kDa modular enzyme that presents the CBM22/GH10/CBM9 architecture found in a subset of large xylanases. We report here the three-dimensional structure of the Xyn10C N-terminal region, containing the xylan-binding CBM22-1–CBM22-2 tandem (Xyn10C-XBD), which represents the first solved crystal structure of two contiguous CBM22 modules. Xyn10C-XBD is folded into two separate CBM22 modules linked by a flexible segment that endows the tandem with extraordinary plasticity. Each isolated domain has been expressed and crystallized, and their binding abilities have been investigated. Both domains contain the R(W/Y)YYE motif required for xylan binding. However, crystallographic analysis of CBM22-2 complexes shows Trp-308 as an additional binding determinant. The long loop containing Trp-308 creates a platform that possibly contributes to the recognition of precise decorations at subsite S2. CBM22-2 may thus define a subset of xylan-binding CBM22 modules directed to particular regions of the polysaccharide. Affinity electrophoresis reveals that Xyn10C-XBD binds arabinoxylans more tightly, which is more apparent when CBM22-2 is tested against highly substituted xylan. The crystal structure of the catalytic domain, also reported, shows the capacity of the active site to accommodate xylan substitutions at almost all subsites. The structural differences found at both Xyn10C-XBD domains are consistent with the isothermal titration calorimetry experiments showing two sites with different affinities in the tandem. On the basis of the distinct characteristics of CBM22, a delivery strategy of Xyn10C mediated by Xyn10C-XBD is proposed.     

Discrimination between distant homologs and structural analogs: lessons from manually constructed, reliable data sets

A natural way to study protein sequence, structure, and function is to put them in the context of evolution. Homologs inherit similarities from their common ancestor, while analogs converge to similar structures due to a limited number of energetically favorable ways to pack secondary structural elements. Using novel strategies, we previously assembled two reliable databases of homologs and analogs. In this study, we compare these two data sets and develop a support vector machine (SVM)-based classifier to discriminate between homologs and analogs. The classifier uses a number of well-known similarity scores. We observe that although both structure scores and sequence scores contribute to SVM performance, profile sequence scores computed based on structural alignments are the best discriminators between remote homologs and structural analogs. We apply our classifier to a representative set from the expert-constructed database, Structural Classification of Proteins (SCOP). The SVM classifier recovers 76% of the remote homologs defined as domains in the same SCOP superfamily but from different families. More importantly, we also detect and discuss interesting homologous relationships between SCOP domains from different superfamilies, folds, and even classes.     

濒危植物七子花的生殖构件特征

对濒危植物七子花(Heptacodium miconioides)的花枝构成及不同类型花序的结实状况进行了研究。结果显示：(1)在黄经洞(种群B),花枝的营养生长旺盛,单枝的花序数和花数多,平均为23．5个和278朵;在狮子岩坑(种群A)．开多轮花的花序比例高．但花枝的花序数较少,单枝的开花数最少。(2)七子花的结实率很低．可育胚珠的平均结实率均在40％左右,且结实率与花序的开花数量呈显著的负相关关系。(3)花序类型对种子重量也有一定的影响,其中种群A的Ⅰ型花序所结果实的种子最大,但这些种子的胚也未发育完全。因此,七子花成为濒危物种的关键并不是结实的数量,而是结实的质量。     

高原医学救援实战演练教学改革实践与分析

医学救援实战演练教学贴近实战,并综合各学科而设,是培养应急性医学救援人才的必备课程。以往演练暴露诸多问题,例如学员不能全面参与训练,学员对突发状况应对能力较弱,训练内容设置不合理以及考核方式不能反映学员训练的真实情况等问题。我们进行高原医学救援演练教学方法改革,采用多用途学习模块,学员全面参与演练科目的方式,整合课堂、临床相关方面知识技能,组织教学训练单元,建立规范化、标准化救治流程,删减调整不相关内容,可在短期内完成培训。最后,通过考核方式改革,采用全程考查并及时对参训人员进行反馈保证训练质量。     

Theory does not meet experiment: transient dynamics changes patterns of exclusion in an intraguild predation system

Population Ecology - Although empirical verifications of ecological theory are essential for the advance of our understanding of ecosystems functioning, they are often hard to obtain or even...     

持留菌及其对微生物膜的耐受性影响研究进展

持留菌（persisters）是细菌种群中所占比例不到0.1%的一类特殊亚群,具有与种群内普通菌、抗性突变菌所不同的特征,其形成机制复杂,不易分离培养.持留菌可通过“休眠-生长-增殖”应对逆境的胁迫,维持自身生存和菌体结构稳定,在生物膜的多药耐受性与多金属耐性中发挥着重要作用,对于维持微生物群落结构稳定具有重要意义.本文从持留菌的研究历程、特点、基因调控机制及其对微生物膜的耐药性与多金属耐性的影响等方面进行了综述,并对今后的研究方向进行了展望.