A dipicolinic acid tag for rigid lanthanide tagging of proteins and paramagnetic NMR spectroscopy

A new lanthanide tag was designed for site-specific labeling of proteins with paramagnetic lanthanide ions. The tag, 4-mercaptomethyl-dipicolinic acid, binds lanthanide ions with nanomolar affinity, is readily attached to proteins via a disulfide bond, and avoids the problems of diastereomer formation associated with most of the conventional lanthanide tags. The high lanthanide affinity of the tag opens the possibility to measure residual dipolar couplings in a single sample containing a mixture of paramagnetic and diamagnetic lanthanides. Using the DNA-binding domain of the E. coli arginine repressor as an example, it is demonstrated that the tag allows immobilization of the lanthanide ion in close proximity of the protein by additional coordination of the lanthanide by a carboxyl group of the protein. The close proximity of the lanthanide ion promotes accurate determinations of magnetic susceptibility anisotropy tensors. In addition, the small size of the tag makes it highly suitable for studies of intermolecular interactions.     

Limit cycles in a continuous fermentation model

The existence of limit cycles in a mathematical model for a continuous fermentation process is investigated. Estimation of perimeters and the relative positions of limit cycles are also discussed.     

THE BÄCKLUND TRANSFORMATION AND NONLINEAR SUPERPOSITION FORMULA OF SOLUTIONS FOR THE LIOUVILLE’S EQUATION IN HIGHER DIMENSIONS

In this paper, we show that Backlund transformation derived by Leibbrandt et al. for the Liouville’s equation in three spatial dimensions, ▽²a=expa, ▽²=-∂_x²+∂_y²+∂_z² can be decomposed into several Backlund transformations for the same equation in two spatial dimensions, moreover, the superposition formula which is derived from this transformation is actually invalid, thus the discussions based on that formula is incorrect as well. We also considered some results about the Liouville’s equation in N spatial dimensions.     

水稻种子萌发期高压诱导的SSH-cDNA文库构建与分析

 为了研究高压处理对高等植物基因表达的影响,以萌发过程中经高压处理后的水稻种子的mRNA作为检测子（Tester）,以对照样品的mRNA作为驱动子（Driver）,采用抑制差减杂交（SSH）结合镜像选择技术（MOS）构建了高压处理后水稻种子萌发过程中诱导表达的差减cDNA文库,并通过蓝白斑筛选获得了580个重组克隆。菌液PCR检测的结果表明这些克隆中的插入片段的大小主要分布在200～1000 bp之间,平均大小约为575 bp,其中单一扩增条带的有效重组克隆数为542个,有效的重组克隆率为93.3%。对部分重组克隆进行测序发现,受高压诱导表达的基因主要涉及到代谢、胁迫响应、转录调控等方面。为高压处理后水稻种子基因表达模式变化的研究打下了基础。     

Novel 3-D Network: From the Reaction of Polyamine with Pyromellitic Dianhydride

Abstract

Under mild condition the reaction of pyromellitic dianhydride with polyamine in methanol solution results in ammonium carboxylate salts rather than amide polymer. X-ray analysis indicates a manifestation of 3-D network linked by N─H⁺…O^? H─N⁺ hydrogen bonding for the three ammonium salts, in which the porous spaces are filled with water molecules.     

Thiol-ene reaction: a versatile tool in site-specific labelling of proteins with chemically inert tags for paramagnetic NMR

Site-specific tagging of proteins with paramagnetic lanthanides generates valuable long-range structure restraints for structural biology by NMR spectroscopy. We show that the thiol-ene addition reaction offers a powerful tool for tagging proteins in a chemically stable manner with very small lanthanide tags.     

Synthesis and thermodynamic properties of novel tripod ligands and their cobalt(II), nickel(II), copper(II) and zinc(II) complexes

Three novel compounds, based on the 1,3,5-benzene core with C₃-symmetry, have been prepared and characterized by elemental analysis, i.r. and ¹H-n.m.r. Thermodynamic properties of the ligands and their Co^II, Ni^II, Cu^II, and Zn^II metal complexes have been investigated and the corresponding stability constants obtained at 25.0 ± 0.1 °C and with I = 0.1 mol dm^–3 in KNO₃ by potentiometric titration. A linear free energy relationship exists between the stability constants of complexes and the protonation constants of ligands in the ternary system of the Cu^II-5-substituted phenanthroline-tripod ligand complexes.     

6-(5'-(8'-羟基喹啉)亚甲基)-1,4,8,11-四氮杂十一烷-5,7-二酮·5-取代邻菲罗啉合铜(Ⅱ)-铜(Ⅱ)或钴(Ⅱ)双核混配体系的稳定性研究

本文合成了8-羟基喹啉取代的二氧四胺开链配体L并进行了红外、元素分析、核磁和质谱表征。在(25±0.1)℃,I=0.1mol·dm     

Rigid,Highly Reactive and Stable DOTA-like Tags Containing a Thiol-Specific Phenylsulfonyl Pyridine Moiety for Protein Modification and NMR Analysis**

Site specific installation of a paramagnetic ion with magnetic anisotropy in a biomolecule generates valuable structural restraints, such as pseudocontact shifts (PCSs) and residual dipolar couplings (RDCs). These paramagnetic effects can be used to characterize the structures, interactions and dynamics of biological macromolecules and their complexes. Two single-armed DOTA-like tags, BrPSPy-DO3M(S)A-Ln and BrPSPy-6M-DO3M(S)A-Ln, each containing a thiol-specific reacting group, that is, a phenylsulfonyl pyridine moiety, are demonstrated as rigid, reactive and stable paramagnetic tags for protein modification by formation of a reducing resistant thioether bond between the protein and the tag. The two tags present high reactivity with the solvent exposed thiol group in aqueous solution at room temperature. The introduction of Br at the meta-position in pyridine enhances the reactivity of 4-phenylsulfonyl pyridine towards the solvent exposed thiol group in a protein, whereas the ortho-methyl group in pyridine increases the rigidity of the tag in the protein conjugates. The high performance of these two tags has been demonstrated in different cysteine mutants of ubiquitin and GB1. The high reactivity and rigidity of these two tags can be added in the toolbox of paramagnetic tags suitable for the high-resolution NMR measurements of biological macromolecules and their complexes.     

Constructing Photoactivatable Protein with Genetically Encoded Photocaged Glutamic Acid

Genetically replacing an essential residue with the corresponding photocaged analogues via genetic code expansion (GCE) constitutes a useful and unique strategy to directly and effectively generate photoactivatable proteins. However, the application of this strategy is severely hampered by the limited number of encoded photocaged proteinogenic amino acids. Herein, we report the genetic incorporation of photocaged glutamic acid analogues in E. coli and mammalian cells and demonstrate their use in constructing photoactivatable variants of various fluorescent proteins and SpyCatcher. We believe genetically encoded photocaged Glu would significantly promote the design and application of photoactivatable proteins in many areas.