抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Signaling Recognition Events with Fluorescent Sensors and Switches.

In the last 10 years the field of molecular diagnostics has witnessed an explosion of interest in the use of nanomaterials in assays for gases, metal ions, and DNA and protein markers for many diseases. Intense research has been fueled by the need for practical, robust, and highly sensitive and selective detection agents that can address the deficiencies of conventional technologies. Chemists are playing an important role in designing and fabricating new materials for application in diagnostic assays. In certain cases assays based upon nanomaterials have offered significant advantages over conventional diagnostic systems with regard to assay sensitivity, selectivity, and practicality. Some of these new methods have recently been reviewed elsewhere with a focus on the materials themselves or as subclassifications in more generalized overviews of biological applications of nanomaterials.1-7 We intend to review some of the major advances and milestones in the field of detection systems based upon nanomaterials and their roles in biodiagnostic screening for nucleic acids, * To whom correspondence should be addressed. Phone: 847-4913907. Fax: 847-467-5123. E-mail: chadnano@northwestern.edu. Nathaniel L. Rosi earned his B.A. degree at Grinnell College (1999) and his Ph.D. degree from the University of Michigan (2003), where he studied the design, synthesis, and gas storage applications of metal−organic frameworks under the guidance of Professor Omar M. Yaghi. In 2003 he began postdoctoral studies as a member of Professor Mirkin’s group at Northwestern University. His current research focuses on the rational assembly of DNA-modified nanostructures into larger-scale materials.

/pdf/nanostructures-in-biodiagnostics-5553cs9yqw.pdf

Nanostructures in Biodiagnostics

Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

/pdf/gold-nanoparticles-in-chemical-and-biological-sensing-5e2qojkdzn.pdf

Gold nanoparticles in chemical and biological sensing.

I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

With the goal of developing artificial nucleases for DNA hydrolysis, metal-coordinating peptides have been tethered to a DNA-intercalating rhodium complex to deliver metal ions to the sugar−phosphate backbone. The intercalator, [Rh(phi)_2bpy‘]Cl_3 [phi = 9,10-phenanthrenequinone diimine; bpy‘ = 4-(butyric acid)-4‘-methyl-2,2‘-bipyridine], provides DNA binding affinity, and a metal-binding peptide contributes reactivity. This strategy for DNA hydrolysis is a general one, and zinc(II)-promoted cleavage has been demonstrated for two widely different tethered metallopeptides. An intercalator coupled with a de novo-designed α helix containing two histidine residues has been demonstrated to cleave both supercoiled plasmid and linear DNA substrates. Mutation of this peptide confirms that the two histidine residues are essential for Zn^(2+) binding and cleavage. Zinc(II)-promoted cleavage of supercoiled plasmid has also been demonstrated with an intercalator−peptide conjugate containing acidic residues and modeled after the active site of the BamHI endonuclease. Other redox-active metals, such as copper, have been delivered to DNA with our intercalator−peptide conjugates to effect oxidative chemistry. Copper cleavage experiments and photocleavage experiments with [Rh(phi)_2bpy‘]^(3+) complement the hydrolysis studies and provide structural information about the interactions between the tethered metallopeptides and DNA. Variation of the rhodium intercalator was also explored, but with a mismatch-specific intercalator, no site-specific hydrolysis was found. These experiments, in which the peptide, the metal cation, and the intercalator components of the conjugate are each varied, illustrate some of the issues involved in creating an artificial nuclease with DNA intercalators and metallopeptides.

http://www.its.caltech.edu/~jkbgrp/abstracts/A200.pdf

DNA hydrolysis and oxidative cleavage by metal-binding peptides tethered to rhodium intercalators.

Potent oxidants which intercalate in DNA serve as tools to probe DNA-mediated electron-transfer reactions. A photoexcited rhodium intercalator, Rh(phi)_2DMB^(3+) (phi = 9,10-phenanthrenequinone diimine and DMB = 4,4‘-dimethyl-2,2‘-bipyridine), tethered to DNA, promotes both oxidative damage to 5‘-GG-3‘ doublets in DNA and the repair of thymine dimers from a remote site on the DNA duplex. DNA-mediated repair of a thymine dimer lesion by charge transfer from the tethered rhodium intercalator is quantitative, albeit with low photoefficiency, occurs in an intraduplex reaction over long range (36 A), and requires that the intervening bases be paired. When both oxidative reactions, repair and oxidative damage, are monitored on the same duplex, competition is evident; the presence of both a 5‘-GG-3‘ site and the thymine dimer diminished the dimer repair efficiency by 20−40% and decreased damage at the 5‘-GG-3‘ sites 2-fold compared to similar sequences lacking either the guanine doublet or thymine dimer, respectively. In addition to damage at the 5‘-G of 5‘-GG-3‘ sites, we also observe oxidation at the 3‘-G of the 5‘-GT TG-3‘ tetrad only in the presence of thymine dimer. Overall, the yield of repaired thymine strand was at least 10 times higher than the yield of oxidized guanine in the same sequences. While the 5-GG-3‘ may represent the thermodynamically favored site for oxidative reaction, repair of the thymine dimer appears to be kinetically more favorable. Dipyridophenanzine (dppz) complexes of ruthenium(III), less potent oxidants which intercalate in DNA, oxidize 5‘-GG-3‘ doublets efficiently but cannot trigger the repair of the thymine dimer lesion. Oxidative damage to DNA from a distance, mediated by the DNA base pair stack, can, however, be utilized to probe the disruption in the base stack generated by the thymine dimer. The presence of the dimer does not diminish oxidation by a Ru(III) intercalator at a distal guanine doublet, suggesting that the disruption caused by the dimer does not block charge transfer through the DNA duplex. DNA-mediated electron-transfer reactions of metallointercalators therefore serve to illustrate important aspects of radical migration and its consequence with respect to reactions at a distance through the DNA base pair stack.

Oxidative charge transfer to repair thymine dimers and damage guanine bases in dna assemblies containing tethered metallointercalators

Chiral probe for A-form helixes of DNA and RNA: tris(tetramethylphenanthroline)ruthenium(II)

The intercalative binding of chiral tris(phenanthroline) metal complexes to DNA is stereo-selective. The enantiomeric selectivity is based upon the differential steric interactions between the two non-intercalating phenanthroline ligands of each isomer with the DNA phosphate backbone. Gel electrophoretic assays of helical unwinding, optical enrichment studies by equilibrium dialysis and luminescence titrations with separated enantiomers of (phen)_3Ru^(2+) all indicate that the delta isomer binds preferentially to the right-handed duplex. The chiral discrimination is governed by the DNA helical asymmetry. Complete stereospecifity is seen with isomers of the bulkier RuDIP (tris-4,7-diphenylphenanthrolineruthenium(II)). While both isomers bind to Z-DNA, a poor template for discrimination, binding of Λ-RuDIP to B-DNA is precluded. These chiral complexes therefore serve as a chemical probe to distinguish left and right-handed DNA helices in solution.

Tris (phenanthroline) Metal Complexes: Probes for DNA Helicity

A cyclometalated complex of Ir(III) is covalently tethered to DNA oligonucleotides and serves as both a photooxidant and photoreductant in the study of DNA-mediated hole transport (HT) and electron transport (ET). Spectroscopic and melting temperature studies support intercalation of the tethered complex into the DNA duplex through the functionalized dppz ligand. Using these tethered assemblies, ET and HT is initiated in DNA by the same photoredox probe. Cyclopropylamine substituted bases, N_4-cyclopropylcytosine (^(CP)C) and N_2-cyclopropylguanine (^(CP)G) are used as kinetically fast electron and hole traps to probe the resulting electron migration processes after direct irradiation of the tethered Ir assembly. Oxidation of ^(CP)G and ^(CP)C is promoted efficiently by HT from photoexcited Ir(III) when the modified bases are positioned in the purine strands of the A-tract. In contrast, when CPC is embedded in a pyrimidine tract, ET to yield reductive decomposition is observed. Thus, the Ir(III)-tethered DNA assembly containing cyclopropyl-modified bases provides a unique model system to explore the two DNA-mediated electron migration processes using the same photoredox probe and the same DNA bridge.

Jacqueline K. Barton

Papers

DNA hydrolysis and oxidative cleavage by metal-binding peptides tethered to rhodium intercalators.

Oxidative charge transfer to repair thymine dimers and damage guanine bases in dna assemblies containing tethered metallointercalators

Chiral probe for A-form helixes of DNA and RNA: tris(tetramethylphenanthroline)ruthenium(II)

Tris (phenanthroline) Metal Complexes: Probes for DNA Helicity

Long-range electron and hole transport through DNA with tethered cyclometalated iridium(III) complexes.