| POLYMERS Vol.62 No.9 |
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COVER STORY
Tackle the Folding of Polymers |
| COVER STORY: Highlight Reviews |
| Recent Development in Design and Function of Artificial Helical Polymers | Naoki OUSAKA, Eiji YASHIMA |
| <Abstract> The helix is one of the most ubiquitous structural motifs in living systems. Therefore, much attention has been paid to construct artificial helical polymers over the last two decades and not only to mimic the structures of biological helices, but also to develop advanced chiral functional materials. In this article, the recent development in the molecular design of helical polymers with a unique function and structural analysis is described. Keywords: Helical Structure / Chirality / Double Helix / Asymmetric Catalyst / Molecular Spring |
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| Ideal and Reality in Protein Folding: Aggregation and Chaperones | Hideki TAGUCHI |
| <Abstract> Proteins function as they fold into unique three-dimensional structures. This review focuses on recent topics on protein folding and molecular chaperones, which assist the protein folding in the cell. Keywords: Protein Folding / Chaperones / Chaperonin / GroEL / Aggregation / Cell-Free Translation |
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| Artificial Molecular Chaperone System | Yoshihiro SASAKI, Kazunari AKIYOSHI |
| <Abstract> Efficient production of a large amount of protein is a major focus of biotechnology and post-genome research fields. However, folding (or refolding) of proteins into the correct active structure is still a problem to be solved, because partially folded intermediates often form irreversible aggregation or inclusion bodies. In living systems, molecular chaperones selectively trap denatured proteins to prevent the aggregation, and then the host chaperone releases the protein in its refolded form with the aid of ATP and another co-chaperone. The molecular chaperone systems inspired us to explore new concepts in designing artificial molecular chaperones to assist protein folding. In this article, we first review the recent progress of chaperoning function using polysaccharide nanogels as an artificial host for proteins, then focus on liposomal chaperone systems for membrane proteins. We also discuss some biomedical application of nanogels utilizing the molecular chaperone-like function of nanogels. Keywords: Polysaccharide Nanogel / Artificial Molecular Chaperone / Membrane Protein / Cell-Free Protein Synthesis |
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| COVER STORY: Topics and Products |
| Controlled Compaction of Atactic Polymer Chains: Another Approach to Macromolecular Folding | Jean-Francçis Lutz |
| <Abstract> Atactic synthetic polymer chains are, in general, amorphous materials in the solid state and in solution. However, when functionalized on their side chains by associating motifs (e.g. crystalline side-chains, self-assembling supramolecular motifs, reactive functions leading to covalent bridges), atactic polymers can be organized into more ordered materials. In particular, structured globular single-chain object can be formed in solution. Such ‘compaction’ approaches follow design principles that are very different from those that govern the folding of natural proteins or synthetic foldamers. Nevertheless, these novel strategies open up very interesting avenues for single-chain materials design. This exciting new field of research is briefly presented in this short review. Keywords: Polymer Folding / Precision Polymers / Sequence-Controlled Polymers / Single-Chain Technology / Single-Chain Particles |
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| Thermal Hysteresis Exhibited by Synthetic Helical Molecule: Memory Effect at Molecular Level | Masanori SHIGENO, Masahiko YAMAGUCHI |
| <Abstract> Thermal hysteresis is a phenomenon, in which different responses occur during heating and cooling. Although bulk materials can exhibit thermal hysteresis by strong and multiple cooperative interactions between molecules, thermal hysteresis at molecular level in nonpolar organic solvents was essentially not known until now. We found that a chiral sulfonamido helicene tetramer forms a helix dimer in 1,3-difluorobenzene, which unfolds to a random coil on heating. This structural change exhibited thermal hysteresis, in which different structures of a helix dimer and a random coil were formed during heating and cooling at the same temperature. The phenomenon was explained by the different populations of helix dimers and random coils at the same temperature, and by the presence of induction periods. Thermal hysteresis is related to the “memory effect”: the molecules memorize their thermal history, whether they were heated or cooled in the past. The model can also explain the “memory effect”. Keywords: Molecular Thermal Hysteresis / Memory Effect / Induction Period / Helicenes / Helix Dimer / Sulfonamides |
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| SNA: A Nucleic Acid Analogue that can Control the Helical Structure by Sequence Design | Hiroyuki ASANUMA, Keiji MURAYAMA, Hiromu KASHIDA |
| <Abstract> We synthesized a unique nucleic acid analogue, Serinol Nucleic Acid (SNA), from a serinol scaffold tethering natural nucleobases through an amide bond. The SNA oligomer that is fully synthesized from four chiral SNA monomers changes its chirality by the sequence design, not by the inherent chirality of monomers: The SNA oligomer with an asymmetric sequence is chiral whereas the symmetric one is achiral. The chirality of the SNA oligomer can be inverted by reversing its sequence, i.e., two enantiomers of SNA oligomers can be synthesized from four monomers with the identical chirality. Interestingly, SNA formed a remarkably stable duplex with a complementary SNA in an antiparallel manner with its helicity depending on the sequence, which is much more stable than the corresponding DNA/DNA or RNA/RNA duplex. More interestingly, SNA also formed a stable duplex both with DNA and RNA, indicating high potential for antisense agents. These unique properties of SNA might provide an insight for why d-ribose was selected as a scaffold for natural nucleic acids. Keywords: Nucleic Acid Analogue / Serinol Nucleic Acid / Chirality / Helicity/ Cross-Pairing / Antisense Agent |
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| Chaperone Function of Organic Nanotube Gels | Naohiro KAMETA |
| <Abstract> Self-organization of synthetic lipids in water produced nanotube hydrogels in the presence of chemically denatured proteins at room temperature, which were able to encapsulate the proteins in the nanotube channel. Decreasing the concentrations of the denaturants induced refolding of part of the encapsulated proteins in the nanotube channel. Changing the pH dramatically reduced electrostatic attraction between the inner surface mainly covered with amino groups of the nanotube channel and the encapsulated proteins. As the result, the refolded proteins were smoothly released into the bulk solution without specific additive agents. This recovery procedure also transformed the encapsulated proteins from an intermediately refolding state to a completely refolded state. Introduction of hydrophobic groups onto the inner surface of the nanotube channel remarkably enhanced the encapsulation and refolding efficiencies. Refolding was also strongly dependent on the inner diameters of the nanotube channels. Thus, the nanotube hydrogels assisted the refolding of the denatured proteins and acted as artificial chaperones. Keywords: Organic Nanotubes / Nanochannel / Self-Organization / Hydrogels / Chaperones / Refolding / Proteins / Enzymes |
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| Polymer Science and I: A Personal Account |
| Where Does a Random-Coil Go? | Daisuke KAWAGUCHI |
| <Abstract> My winding life has been just like a contour of a random-coil polymer so far. In this essay, I write my personal and research backgrounds and my ambition for the future. |
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| Front-Line Polymer Science |
| Covalent Nanoarchitectures with Well-Defined Nanostructures Produced by Interfacial Reactions | Masashi KUNITAKE |
| <Abstract> The construction of sophisticated, supramolecular architectures through self-assembly has attracted considerable attention as “bottom-up” nanotechnology. The pursuit of methods for design and preparation of robust nanoarchitectonic systems with integrated various functionality through bottom-up methodologies remains a driving force in molecular nanotechnology. Novel polymer materials bearing unique well-defined chemical structures prepared by chemical reaction at the interfaces are introduced. Thermodynamic self-assembly of 1-D and 2-D π-conjugated covalent nanoarchitectures were independently achieved by thermal treatment in ultra high vacuum and “on-site” equilibrium successive polymerization at solid-liquid interfaces. Keywords: Bottom-up Nanotechnology / Soft Solution Process / Covalent Organic Framework / Thermodynamic Self-Assembly / UHV / STM |
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