植物甲基化类黄酮及其O-甲基转移酶研究进展

植物类黄酮是重要的药用成分,其生物学功能与化学结构密切相关.O-甲基化修饰可提高类黄酮的稳定性、蛋白亲和力和生物利用度,从而增强其药用活性.O-甲基转移酶(O-methyltransferase)催化类黄酮合成O-甲基化衍生物,是类黄酮代谢途径中的关键修饰酶.本文综述了植物O-甲基化类黄酮的化学结构、药用功能及其药用价...     

蛋白分子O-糖基化的研究进展

蛋白分子的氧连接糖基化（O-糖基化）修饰是生物体内必不可少的转录后化学修饰之一,其作用方式类似磷酸化,并且两者之间相互作用,共同调节生物大分子的活性。O-糖基化修饰在生物体的转录、翻译、核运输、细胞骨架的形成以及调节细胞器的功能中发挥着重要的作用。通过影响细胞信号的传导,在细胞吞噬、炎性细胞的迁移以及细胞内大分子物质的循环中也起着重要作用。该文主要通过介绍蛋白分子O-糖基化修饰的基础理论以及。一糖基化修饰作用的几个方面,来简要阐述O-糖基化修饰在生物体内发挥的作用。     

高等植物纤维素合成的最新研究进展

继１９９６年从棉花和水稻中克隆出β－葡糖基转移酶基因ｃｅｌ Ａ后，１９９８年又从拟南芥细胞壁突变体中鉴定出了ｃｅｌ Ａ的同源基因ＲＳＷ１。这两项研究充分表明，ｃｅｌ Ａ与高等植物的纤维素合成有关。ｃｅｌ类（ｃｅｌ Ａ－ｌｉｋｅ）超基因家族的蛋白质都具有与底物相结合和催化有关的保守功能域。纤维素离体合成方面的研究进展虽然揭示了包括纤维素在内的多糖生物合成机制的某些方面，但活体的纤维素合成还涉及许多其     

植物富含半胱氨酸蛋白的研究进展

富含半胱氨酸蛋白(cystein-rich proteins,CRPs)是动植物中广泛存在的一类小的分泌性蛋白,具有广泛的生物学功能,如防御、蛋白酶抑制、重金属解毒等。人们在深入研究植物CRPs防御功能的同时,发现CRPs还参与调节植物的生长、发育、生殖等。本文综述了植物CRPs的分类、结构及其在植物生长发育、生殖信号转导等方面的研究进展。     

植物富含半胱氨酸蛋白的研究进展

富含半胱氨酸蛋白（cystein-rich proteins,CRPs）是动植物中广泛存在的一类小的分泌性蛋白,具有广泛的生物学功能,如防御、蛋白酶抑制、重金属解毒等。人们在深入研究植物CRPs防御功能的同时,发现CRPs还参与调节植物的生长、发育、生殖等。本文综述了植物CRPs的分类、结构及其在植物生长发育、生殖信号转导等方面的研究进展。     

大肠杆菌代谢工程改造合成L-高丝氨酸及其衍生物研究进展

l-高丝氨酸及其衍生物(O-琥珀酰-l-高丝氨酸和O-乙酰-l-高丝氨酸)是生物合成l-甲硫氨酸的前体,同时也是合成多种C4化合物(异丁醇、g-丁内酯、1,4-丁二醇、2,4-二羟基丁酸等)和l-草铵膦等的平台化合物。因此,发酵法生产l-高丝氨酸及其衍生物成为近年内研究的热点。然而,利用生物法合成l-高丝氨酸及其衍生物仍存在一些不足之处,如发酵产量不高或糖酸转化率过低等。此外,对l-高丝氨酸及其衍生物合成的总体代谢和调控机制鲜有报道。本文综述了大肠杆菌代谢工程改造合成l-高丝氨酸及其衍生物O-琥珀酰-l-高丝氨酸和O-乙酰-l-高丝氨酸的研究进展,从底物摄取、关键节点碳流分配改造、辅酶NADPH的循环供应以及目标产物的外运输出等方面,系统分析了大肠杆菌全发酵法生产l-高丝氨酸及其衍生物的代谢途径及改造策略,为其后续代谢改造及生物法生产提供一定的研究思路。     

共表达SHMT和TPase载体的构建及双酶法合成L-色氨酸

利用重组大肠杆菌表达丝氨酸羟甲基转移酶(SHMT)和色氨酸酶(TPase),并利用双酶法合成L-色氨酸。采用PCR从大肠杆菌K12基因组中扩增上述两种酶的基因,利用pET-28a载体,构建单表达重组质粒pET-SHMT、pET-TPase和共表达重组质粒pET-ST。将上述3种重组质粒转入大肠杆菌BL21(DE3)进行表达。SDS-PAGE结果表明,单表达基因工程菌BL21(DE3)/pET-SHMT和BL21(DE3)/pET-TPase分别在47kDa(SHMT)和50kDa(TPase)处有蛋白表达带;共表达基因工程菌BL21(DE3)/pET-ST在上述两处均有蛋白表达带。与宿主菌相比,单表达SHMT基因工程菌产酶活性提高了6.4倍;单表达TPase基因工程菌产酶活性提高了8.4倍;共表达SHMT和TPase基因工程菌产酶活性分别提高了6.1和6.9倍。利用工程菌所产酶进行双菌双酶法和单菌双酶法合成L-色氨酸。两菌双酶合成L-色氨酸的累积量达到41.5g/L,甘氨酸转化率为83.3%,吲哚转化率为92.5%;单菌双酶合成L-色氨酸的累积量达到28.9g/L,甘氨酸转化率为82.7%,吲哚转化率为82.9%。     

植物腺毛中防御物质的合成与调控及转运研究进展

植物毛状体来源于表皮细胞的延伸,是表皮细胞的特有结构。植物毛状体可分为腺毛和非腺毛,腺毛是具有分泌作用的毛状体,也是大量次生代谢产物的合成、储存以及释放的场所。植物腺毛常分泌不同类型的防御物质如萜类、氨基酸及苯丙烷类、酰基糖、脂肪类衍生物等,这些次生代谢物质能够保护植物免受生物和非生物胁迫,具有重要的防御作用。该文对近年来国内外有关植物腺毛的类型、防御物质的合成与调控等方面的研究进展进行综述,并重点对其合成途径、调控机理与转运机制的研究进展进行梳理,以期为防御物质的生物合成和遗传改良研究提供参考。     

植物淀粉生物合成调节机制的研究进展

淀粉是植物光合作用固定碳形成的主要碳水化合物,不仅在植物的整个生长发育过程中具有重要的生理作用,而且对于新型清洁生物能源的开发利用具有非常巨大的经济价值。本文概述了植物淀粉的合成途径及其合成调控机制的相关研究进展。     

植物油脂合成调控的研究进展

植物种子是人们日常生活所需油脂的重要来源。近年来研究者对植物种子的研究阐明了油脂合成的机理,并挖掘了一些调控合成途径的关键酶和基因。在前人研究的基础之上,补充了成油途径、成油相关基因、转录调控等方面的进展,并从碳源供应、转运及胚乳的影响等方面概述了它们可能对植物油脂形成的影响。     

Cysteine scanning mutagenesis of putative transmembrane helices IX and X in the lactose permease of Escherichia coli.

Using a functional lactose permease mutant devoid of Cys residues (C-less permease), each amino-acid residue in putative transmembrane helices IX and X and the short intervening loop was systematically replaced with Cys (from Asn-290 to Lys-335). Thirty-four of 46 mutants accumulate lactose to high levels (70-100% or more of C-less), and an additional 7 mutants exhibit lower but highly significant lactose accumulation. As expected (see Kaback, H.R., 1992, Int. Rev. Cytol. 137A, 97-125), Cys substitution for Arg-302, His-322, or Glu-325 results in inactive permease molecules. Although Cys replacement for Lys-319 or Phe-334 also inactivates lactose accumulation, Lys-319 is not essential for active lactose transport (Sahin-Tóth, M., Dunten, R.L., Gonzalez, A., & Kaback, H.R., 1992, Proc. Natl. Acad. Sci. USA 89, 10547-10551), and replacement of Phe-334 with leucine yields permease with considerable activity. All single-Cys mutants except Gly-296 --> Cys are present in the membrane in amounts comparable to C-less permease, as judged by immunological techniques. In contrast, mutant Gly-296 --> Cys is hardly detectable when expressed at a relatively low rate from the lac promoter/operator but present in the membrane in stable form when expressed at a high rate from T7 promoter. Finally, studies with N-ethylmaleimide (NEM) show that only a few mutants are inactivated significantly. Remarkably, the rate of inactivation of Val-315 --> Cys permease is enhanced at least 10-fold in the presence of beta-galactopyranosyl 1-thio-beta-D-galactopyranoside (TDG) or an H+ electrochemical gradient (delta mu-H+). The results demonstrate that only three residues in this region of the permease -Arg-302, His-322, and Glu-325-are essential for active lactose transport. Furthermore, the enhanced reactivity of the Val-315 --> Cys mutant toward NEM in the presence of TDG or delta mu-H+ probably reflects a conformational alteration induced by either substrate binding or delta mu-H+.     

禾本科植物EST的研究进展

禾本科作物与人类密切相关,对其分子水平上的研究具有重要的理论和实践意义。EST技术的产生和不断完善为禾本科植物的研究带来了新的思路,迅速推动禾本科植物研究工作的进行。本文综述了EST技术在禾本科植物研究中的应用,包括EST分子标记、构建遗传学图谱、比较基因组学、发现与克隆新基因、基因表达研究以及DNA芯片技术等,并对EST在禾本科植物研究中存在的问题及应用前景进行了分析。     

D-半胱氨酸盐酸盐制备研究

D-半胱氨酸盐是手性药物,主要是第三代头孢抗生素药物—头孢米诺钠的重要中间体。本文介绍了D-半胱氨酸盐酸盐的研制。采用L-半胱氨酸盐酸盐为出发原料,经消旋、沉淀异构体、结晶分离、提纯的方法,制成达到日本味之素公司1997年公布的产品质量指标的D-半胱氨酸盐酸盐。     

Cysteine scanning mutagenesis of the N-terminal 32 amino acid residues in the lactose permease of Escherichia coli.

Using a functional lactose permease mutant devoid of Cys residues (C-less permease), each amino acid residue in the hydrophilic N-terminus and the first putative transmembrane helix was systematically replaced with Cys (from Tyr-2 to Trp-33). Twenty-three of 32 mutants exhibit high lactose accumulation (70-100% or more of C-less), and an additional 8 mutants accumulate to lower but highly significant levels. Surprisingly, Cys replacement for Gly-24 or Tyr-26 yields fully active permease molecules, and permease with Cys in place of Pro-28 also exhibits significant transport activity, although previous mutagenesis studies on these residues suggested that they may be required for lactose transport. As expected, Cys replacement for Pro-31 completely inactivates, in agreement with previous findings indicating that "helix-breaking" propensity at this position is necessary for full activity (Consler TG, Tsolas O, Kaback HR, 1991, Biochemistry 30:1291-1297). Twenty-nine mutants are present in the membrane in amounts comparable to C-less permease, whereas membrane levels of mutants Tyr-3-->Cys and Phe-12-->Cys are slightly reduced, as judged by immunological techniques. Dramatically, mutant Phe-9-->Cys is hardly detectable when expressed from the lac promoter/operator at a relatively low rate, but is present in the membrane in a stable form when expressed at a high rate from the T7 promoter. Finally, studies with N-ethylmalemide show that 6 Cys-replacement mutants that cluster at the C-terminal end of putative helix I are inactivated significantly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional Importance of the Carboxyl Tail Cysteine Residues in the Human D1 Dopamine Receptor

Abstract: To assess the importance of the cysteine residues Cys³⁴⁷ and Cys³⁵¹ in the carboxylic tail in the human D₁ dopamine receptor, seven mutant receptors were constructed by PCR. The pharmacological and functional properties of the wild-type and mutant receptors were assessed following transient expression in COS-7 cells. Affinities for [³H]SCH 23390 of mutant S347 (Cys³⁴⁷→ Gly), T348 (Tyr³⁴⁸→ stop), S351 (Cys³⁵¹→ Gly), T351 (Cys³⁵¹→ stop), T352 (Pro³⁵²→ stop), and S347/S351 (Cys³⁴⁷→ Gly and Cys³⁵¹→ Gly) were similar to that of wild-type receptor, whereas the expression levels were reduced up to 80%. The potency of dopaminergic antagonists for these mutant receptors was very similar to that of the wild-type receptor. However, mutant T347 (Cys³⁴⁷→ stop) showed a 15–25-fold reduced affinity for the antagonists SCH 23390, (+)-butaclamol, and cis-flupentixol, thus not allowing radioligand analysis. Wild-type and mutant receptors responded dose-dependently with similar potency to dopamine and SKF 38393 with an increased adenylyl cyclase activity. However, mutant receptors with the Cys³⁴⁷ residue changed or removed displayed a diminished ability to activate adenylyl cyclase. Dopamine preexposure desensitized wild-type and mutant S351 receptors. However, mutant receptors with Cys³⁴⁷ replaced or the distal part of the carboxyl tail removed were unable to desensitize. Thus, Cys³⁴⁷ in the cytoplasmic tail of the human D₁ dopamine receptor is important for the receptor in maintaining the conformation for antagonist binding, to play a crucial role in activation of adenylyl cyclase, and to be essential for agonist-induced desensitization.     

植物种子油合成的调控与遗传修饰

植物种子油含有多种脂肪酸,是一种重要的种子贮藏化舍物。种子油既是人类的食品,又是重要的工业原料。代谢物组学的发展加深了对种子油生物合成途径的全景式认识,应用基因工程改良种子油品质和价值的研究已取得长足的进展。本文分析了种子油及脂肪酸合成调控机制的复杂性,论述了转基因提高种子油及高营养品质脂肪酸含量和培育能大量合成积累工业用脂肪酸的油料作物的技术策略、存在问题和发展前景。     

Cysteine Racemization in Peptide Synthesis: A New and Easy Detection Method

A new method has been developed for the rapid determination of D-cysteine contents in synthetic peptides. It is based on the reduction of cystine residues, when present, with tris- alkylphosphines, selective derivatization of the cysteine residues with 4-vinylpyridine, followed by acid hydrolysis of the (4-pyridylethyl)cysteine –peptides. Baseline enantiomeric resolution of theD ,L -S-β-(4-pyridylethyl)cysteine, and thus quantification ofD - enantiomer contents at levels ≤1%, is easily achieved by capillary zone electrophoresis exploiting the host–guest complexation principle with crown ethers or by gas chromatography on chiral glass capillary columns upon conventional derivatization of the hydrolysate. The acid-stability of the (4-pyridylethyl)cysteine derivative prevents racemization via thiazoline intermediates and allows for standardization of the acid hydrolysis-dependent racemization.     

植物细胞壁中纤维素合成的研究进展

纤维素是植物细胞壁的主要成分,是植物细胞壁执行生理功能的基础,也是人类生产和生活中必不可少的一类物质。本文对纤维素合成、合成中所需要的酶以及纤维素沉积中微纤丝的作用等方面进行了综述和探讨, 并对纤维素合成的深入研究进行了展望。