Popular science articles: July 2013

Herpes Virus Genome, The Pressure Is On

David W. Bauer †, Jamie B. Huffman ‡, Fred L. Homa ‡, and Alex Evilevitch *†§

† Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States

‡ Department of Microbiology and Molecular Genetics,University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260 United States

§ Department of Biochemistry and Structural Biology,Lund University, 221 00 Lund, Sweden

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja404008r

Publication Date (Web): July 5, 2013

Herpes simplex virus type 1 (HSV-1) packages its micrometers-long double-stranded DNA genome into a nanometer-scale protein shell, termed the capsid. Upon confinement within the capsid, neighboring DNA strands experience repulsive electrostatic and hydration forces as well as bending stress associated with the tight curvature required of packaged DNA. By osmotically suppressing DNA release from HSV-1 capsids, we provide the first experimental evidence of a high internal pressure of tens of atmospheres within a eukaryotic human virus, resulting from the confined genome. Furthermore, the ejection is progressively suppressed by increasing external osmotic pressures, which reveals that internal pressure is capable of powering ejection of the entire genome from the viral capsid. Despite billions of years of evolution separating eukaryotic viruses and bacteriophages, pressure-driven DNA ejection has been conserved. This suggests it is a key mechanism for viral infection and thus presents a new target for antiviral therapies.

Reorientation of a Single Bond within an Adsorbed Molecule by Tunneling Electrons

Jörg Henzl †, Konrad Boom †, and Karina Morgenstern *‡

† Abteilung für Atomare und Molekulare Strukturen (ATMOS), Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, D-30167 Hannover, Germany

‡ Lehrstuhl für Physikalische Chemie I, Ruhr-Universität Bochum, D-44780 Bochum, Germany

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja405809f

Publication Date (Web): July 25, 2013

Scanning tunneling microscopy offers the exciting possibility to manipulate individual molecules by vibrational excitation via inelastically tunneling electrons. The electrons transfer energy into molecular vibrational modes, leading to breakage or formation of individual bonds. It is challenging to precisely control intramolecular changes by this process. We demonstrate that for 4,4′-dihydroxyazobenzene adsorbed on Au(111) or Ag(111), the manipulation facilitates rotation of the OH end groups around the C–O bond between metastable states; this corresponds to a reorientation of the hydrogen, the ultimate limit of a conformational change within a molecule.

Nucleation-Controlled Polymerization of Nanoparticles into Supramolecular Structures

Jing Wang †, Hongwei Xia §, Yanfeng Zhang ‡, Hua Lu ‡, Ranjan Kamat †, Andrey V. Dobrynin †,Jianjun Cheng ‡, and Yao Lin *†§

†Polymer Program, Institute of Materials Science and§Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, United States

‡ Department of Materials Science and Engineering,University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja402757e

Publication Date (Web): May 22, 2013

Controlled assembly of inorganic nanoparticles (NPs) into structurally defined supramolecular polymers will create nanomaterials with new collective properties. However, supramolecular polymerization of isotropic NPs remains a challenge because of the lack of anisotropic interactions in these monomers to undergo directional associations for the cooperative growth of supramolecular chains. Herein we report self-assembly behavior of poly(l-glutamic acid)-grafted gold NPs in solution and describe how combined attractive and repulsive interactions influence the shape and size of the resulting supramolecular assemblies. The study shows that the chain growth of supramolecular polymers can be achieved from the NP monomers and the process occurs in two distinct stages, with a slow nucleation step followed by a faster chain propagation step. The resulting supramolecular structures depend on both the grafting density of the poly(l-glutamic acid) on the NPs and the size of the NPs.

A Sugar-Functionalized Amphiphilic Pillar[5]arene: Synthesis, Self-Assembly in Water, and Application in Bacterial Cell Agglutination

Guocan Yu †, Yingjie Ma †, Chengyou Han †, Yong Yao †, Guping Tang §, Zhengwei Mao ‡, Changyou Gao ‡, and Feihe Huang *†

†Department of Chemistry and ‡Department of Polymer Science and Engineering, MOE Key Laboratory of Macromolecular Synthesis and Functionalization,Zhejiang University, Hangzhou 310027, P. R. China

§ Department of Chemistry, Institute of Chemical Biology and Pharmaceutical Chemistry, Zhejiang University, Hangzhou 310027, P. R. China

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja405237q

Publication Date (Web): June 24, 2013

A novel sugar-functionalized amphiphilic pillar[5]arene containing galactose groups as the hydrophlic part and alkyl chains as the hydrophobic part was designed and synthesized. It self-assembles in water to produce nanotubes as confirmed by TEM, SEM, and fluorescence microscopy. These nanotubes, showing low toxicity to both cancer and normal cells, can be utilized as excellent cell glues to agglutinate E. coli. The existence of galactoses on these nanotubes provides multivalent ligands that have high affinity for carbohydrate receptors onE. coli.

Modulation of In-Membrane Receptor Clustering upon Binding of Multivalent Ligands

Anna Grochmal †, Elena Ferrero †, Lilia Milanesi ‡, and Salvador Tomas *†

† Institute of Structural and Molecular Biology and Department of Biological Sciences, School of Science,Birkbeck University of London, Malet Street, London WC1E 7HX, U.K.

‡ School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, U.K.

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja404428u

Publication Date (Web): June 13, 2013

In living cells and biomimetic systems alike, multivalent ligands in solution can induce clustering of membrane receptors. The link between the receptor clustering and the ligand binding remains, however, poorly defined. Using minimalist divalent ligands, we develop a model that allows quantifying the modulation of receptor clustering by binding of ligands with any number of binding sites. The ligands, with weak binding affinity for the receptor and with binding sites held together by flexible linkers, lead to nearly quantitative clustering upon binding in a wide range of experimental conditions, showing that efficient modulation of receptor clustering does not require pre-organization or large binding affinities per binding site. Simulations show that, in the presence of ligands with five or more binding sites, an on/off clustering response follows a very small change in receptor density in the membrane, which is consistent with the highly cooperative behavior of multivalent biomolecular systems.

Bioinspired Artificial Single Ion Pump

Huacheng Zhang †, Xu Hou ‡, Lu Zeng §, Fu Yang §,Lin Li §, Dadong Yan

, Ye Tian *†, and Lei Jiang *†

† Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China

‡ National Center for Nanoscience and Technology, Beijing 100190, P. R. China

§College of Chemistry and

Department of Physics,Beijing Normal University, Beijing 100875, P. R. China

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja4037669

Publication Date (Web): June 17, 2013

Bioinspired artificial functional nanochannels for intelligent molecular and ionic transport control at the nanoscale have wide potential applications in nanofluidics, energy conversion, and biosensors. Although various smart passive ion transport properties of ion channels have been artificially realized, it is still hugely challenging to achieve high level intelligent ion transport features in biological ion pumps. Here we show a unique bioinspired single ion pump based on a cooperative pH response double-gate nanochannel, whose gates could be opened and closed alternately/simultaneously under symmetric/asymmetric pH environments. With the stimulation of the double-gate nanochannel by continuous switching of the symmetric/asymmetric pH stimuli, the bioinspired system systematically realized three key ionic transport features of biological ion pumps, including an alternating gates ion pumping process under symmetric pH stimuli, transformation of the ion pump into an ion channel under asymmetric pH stimuli, and a fail-safe ion pumping feature under both symmetric and asymmetric pH stimuli. The ion pumping processes could well be reproduced under a concentration gradient. With the advantages of the extraordinary ionic transport functions of biological ion pumps, the bioinspired ion pump should find widespread applicability in active transportation-controlling smart nanofluidic devices, efficient energy conversions, and seawater desalinization, and open the way to design and develop novel bioinspired intelligent artificial nanochannel materials.

Tissue engineering: How to build a heart

With thousands of people in need of heart transplants, researchers are trying to grow new organs.

How Far Can a Sodium Ion Travel within a Lipid Bilayer?

François Otis , Charles Racine-Berthiaume , and Normand Voyer *

Département de Chimie and PROTEO, Faculté des Sciences et de Génie, Université Laval, Pavillon Alexandre-Vachon, 1045 avenue de la Médecine, Québec, QC, Canada, G1V 0A6

J. Am. Chem. Soc., 2011, 133 (17), pp 6481–6483

DOI: 10.1021/ja110336s

Publication Date (Web): March 8, 2011

Analogues of a synthetic ion channel made from a helical peptide were used to study the mechanism of cation translocation within bilayer membranes. Derivatives bearing two, three, four, and six crown ethers used as ion relays were synthesized, and their transport abilities across lipid bilayers were measured. The results showed that the maximum distance a sodium ion is permitted to travel between two binding sites within a lipid bilayer environment is 11 Å.

Direct Quantitation of Peptide-Mediated Protein Transport across a Droplet–Interface Bilayer

Jing Huang , Max Lein , Christopher Gunderson , and Matthew A. Holden

Department of Chemistry, University of Massachusetts, 710 North Pleasant Street, Amherst, Massachusetts 01003, United States

J. Am. Chem. Soc., 2011, 133 (40), pp 15818–15821

DOI: 10.1021/ja2046342

Publication Date (Web): August 12, 2011

We introduce a new method for monitoring and quantitating the transport of materials across a model cell membrane. As a proof-of-concept, the cell-penetrating peptide, Pep-1, was used to carry horseradish peroxidase (HRP) across droplet–interface bilayers (DIBs). Two submicroliter, lipid-encased aqueous droplets form a membrane at the contacting interface, through which enzyme–peptide complexes pass during transport. Following transport, the droplets are separated and the captured enzymes are assayed by a fluorogenic reaction. The DIB method recapitulates the findings of earlier studies involving Pep-1, including the dependence of protein transport on voltage and membrane charge, while also contributing new insights. Specifically, we found that leaflet charge symmetry may play a role in Pep-1-mediated protein translocation. We anticipate that the DIB method may be useful for a variety of transport-based studies.