Molecular basis of photoprotection and control of photosynthetic light-harvesting

In order to maximize their use of light energy in photosynthesis, plants have molecules that act as light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion into a chemical form takes place. The functioning of the antenna responds to the extreme changes in the intensity of sunlight encountered in nature. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight, much of the energy absorbed is not needed and there are vitally important switches to specific antenna states, which safely dissipate the excess energy as heat. This is essential for plant survival, because it provides protection against the potential photo-damage of the photosynthetic membrane. But whereas the features that establish high photosynthetic efficiency have been highlighted, almost nothing is known about the molecular nature of the dissipative states. Recently, the atomic structure of the major plant light-harvesting antenna protein, LHCII, has been determined by X-ray crystallography. Here we demonstrate that this is the structure of a dissipative state of LHCII. We present a spectroscopic analysis of this crystal form, and identify the specific changes in configuration of its pigment population that give LHCII the intrinsic capability to regulate energy flow. This provides a molecular basis for understanding the control of photosynthetic light-harvesting.     

Temperature-induced dissociation reaction and dynamics of light-harvesting complex II isolated from purple photosynthetic bacterium Rps.palustris

Steady-state absorption spectroscopy,circular dichroism,and resonance Raman spectroscopy have been used to investigate the thermal stability of LH2 complex isolated from purple photosynthetic bacterium Rps.palustris.The results show that:1)upon increasing the temperature,a transition from B800 and B850 to free bacteriochlorophyll(B780)happens;2)a gradual decrease and disappearance of CD signal in visible region occur;3)a shift of the frequency,belonging to C==C and C—C stretching vibration,to higher wavenumber takes place.It is suggested that LH2 complex can be dissociated in the presence of B800,B850 and carotenoids simultaneously.Single-exponential fitting on the dynamic decay curves gives the apparent time constants of hundreds of minutes for various pigments.     

细菌光敏色素AphA的克隆表达及重组新方法

通过PCR技术，从蓝藻PCC7120中扩增出细菌光敏色素Apha的基因aphA，进而构建aphA的缺失突变体aphA(N-25/C-445)．二者分别转人表达载体pET30a中，在宿主菌中获得高效表达，获得的脱辅基蛋白与CpcA进行体外重组．在本体外重组体系中，以藻蓝蛋白α亚基(CpeA)，在光敏色素自身作用或者藻蓝蛋白裂合酶的帮助下从CpcA上捕获胆色素完成重组．藻蓝蛋白裂合酶CpcE／F能很大程度增强光敏色素脱辅基蛋白从CocA夺取PCB的能力．该结果对于研究细菌光敏色素的色素来源及生理生化机理都具有重要意义．     

Cloning and characterization of a gene encoding cysteine proteases from senescent leaves of Gossypium hirsutum

A gene encoding a cysteine proteinase was isolated from senescent leave of cotton (Gossypium hirsutum) cv liaomian No. 9 by utilizing rapid amplification of cDNA end spolymerase chain reaction (RACE-PCR), and a set of consensus oligonucleotide primers was designed to anneal the conserved sequences of plant cysteine protease genes. The cDNA, which designated Ghcysp gene, contained 1368 bp terminating in a poly(A)^ trail, and included a putative 5‘(98 bp) and a 3‘(235 bp) non-coding region. The opening reading frame (ORF) encodes polypeptide 344 amino acids with the predicted molecular mass of 37.88 kD and theoretical pl of 4.80. A comparison of the deduced amino acid sequence with the sequence in the GenBank database has shown considerable sequence similarity to a novel family of plant cysteine proteases. This putative cotton Ghcysp protein shows from 67% to 82% identity to the other plants. All of them share catalytic triad of residues, which are highly conserved in three regions. Hydropaths analysis of the amino acid sequence shows that the Ghcysp is a potential membrane protein and localizes to the vacuole, which has a transmembrane helix between resides 7-25. A characteristic feature of Ghcysp is the presence of a putative vacuole-targeting signal peptide of 19-amino acid residues at the N-terminal region. The expression of Ghcysp gene was determined using northern blot analysis. The Ghcysp mRNA levels are high in development senescent leaf but below the limit of detection in senescent root, hypocotyl, faded flower, 6 d post anthesis ovule, and young leaf.     

铜绿微囊藻气囊蛋白GvpW的异源表达纯化与晶体生长研究

铜绿微囊藻(Microcystisaeruginosa PCC 7806)是我国淡水湖泊生态系统季节性蓝藻水华爆发的最优势藻种,其爆发的机制之一在于气囊,它是一种充满气体的蛋白质性质的亚细胞器结构,可为藻细胞提供浮力,调节藻细胞在水体中的位置以利于生长和后续的生境殖民化。铜绿微囊藻的气囊合成涉及14个气囊蛋白,但大部分气囊蛋白在气囊合成过程中的具体分子功能尚不清楚。对其中一个气囊蛋白GvpW进行了分子克隆,利用原核表达系统在体外进行了异源表达,结合镍柱亲和层析和凝胶过滤层析纯化出了高纯度的GvpW,运用动态光散射和化学交联证实在体外纯化后的GvpW是呈单体状态,同时通过晶体初筛和优化获得了生长较好的蛋白质晶体。这为后续解析GvpW的三维结构及在分子水平直观探讨其在气囊合成中的生理功能奠定了基础。     

基于自适应阈值的棉网图像中结杂的识别

在棉网图像中,棉结和杂质(简称结杂)大多都混杂在聚集的纤维网中难以检出和识别.针对这一问题,提出了一种将最大类间方差法(Otsu法)与线性回归相结合的棉网图像结杂分割方法.首先对棉网图像进行预处理,然后根据Otsu法获取棉网图像与背景分开的阈值,再根据线性回归找出该阈值与结杂灰度的关系,获得结杂分割的最佳阈值,从而实现结杂的识别.     

脉冲超声辅助提取双低菜籽蛋白的试验

以传统菜籽加工工艺制得的脱脂双低菜籽饼粕为原料,用脉冲超声辅助提取技术制备双低菜籽蛋白,由单因素试验和正交试验确定的最佳提取工艺参数为:pH=12,超声功率875 W,料液比1∶35 (g/mL),提取时间85 min,料液温度48±3 ℃,脉冲超声工作时间3 s,间歇时间2 s.在此条件下,菜籽蛋白的提取率为83.97%.在pH=4.5的条件下进行菜籽蛋白的沉淀,测得提取产物的得率为52.18%,产物中蛋白的质量分数为68.18%.与传统碱法相比,在提取液的pH值、温度和料液比取值相当的情况下,脉冲超声辅助提取蛋白的提取率提高了38.04%,得率提高了94.56%,提取时间缩短了15%,提取物中蛋白质质量分数显著优于传统碱法.提取产物中硫甙质量分数为0.06%,远远低于国家相关标准(w(硫甙)＜1.85%).     

甘氨酸、赖氨酸、酪氨酸、蛋氨酸在棘孢小单孢菌中的作用

在棘孢小单孢菌(Micromonospora echinospora)突变株(Fzu-707)产生小诺霉素的过程中,运用正交设计筛选小诺霉素(Micronomicin, MCR)生物合成促进剂--氨基酸.经摇瓶实验证明在原培养基中添加一定量的甘氨酸、赖氨酸、酪氨酸、蛋氨酸有利于生物合成小诺霉素,在旋转摇床上220 r/min 36 ℃培养,发酵时间由原工艺144 h缩短到104 h,产量(u·mL-1)较对照可增加20%左右,产素率(u·mL-1·h-1))提高60%左右.