Article

Electrophoresis of a soft toroid of nonuniform structure

Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan.
Colloids and surfaces B: Biointerfaces (Impact Factor: 4.29). 05/2012; 98:36-42. DOI: 10.1016/j.colsurfb.2012.04.019
Source: PubMed

ABSTRACT The electrophoresis of a nonuniformly structured soft particle is modeled theoretically by considering an isolated soft toroid comprising a rigid core and a polyelectrolyte layer with exponential segment distribution. The influences of the thickness of double layer, and the fixed charge density, the friction coefficient, the uniformity, and the thickness of the polyelectrolyte layer on the electrophoresis behavior of the toroid are examined. We show that for a specified fixed charge density, the electrophoresis mobility of the toroid increases with increasing double layer thickness, and the higher that density the larger the mobility. The thicker the polyelectrolyte layer and/or more uniform the segment distribution of that layer the higher the fixed charge density, yielding a larger mobility. The thicker the double layer the more significant is the influence of the polyelectrolyte layer structure of a toroid on its mobility.

0 Followers
 · 
103 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: RECENT studies have revealed that the packaging of DNA into phage heads is an ordered sequence of structural and biochemical events rather than a simple, spontaneous self-assembly of component molecules. In the assembly of T7 for example1, heads containing the products of genes 8-10 and 14-16 are apparently formed first. Gene 9 protein is removed from the heads before or during the incorporation of DNA. At least two other gene products which play no direct structural role are required for the maturation of the heads. A somewhat similar situation exists for phage λ, which has been shown to require ATP for the in vitro packaging of DNA into preformed heads (petite λ)2.
    Nature 02/1976; 259(5541):333-5. DOI:10.1038/259333a0 · 42.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Studies of the organization of double-stranded DNA within bacteriophage heads during the past four decades have produced a wealth of data. However, despite the presentation of numerous models, the true organization of DNA within phage heads remains unresolved. The observations of toroidal DNA structures in electron micrographs of phage lysates have long been cited as support for the organization of DNA in a spool-like fashion. This particular model, like all other models, has not been found to be consistent will all available data. Recently we proposed that DNA within toroidal condensates produced in vitro is organized in a manner significantly different from that suggested by the spool model. This new toroid model has allowed the development of an alternative model for DNA organization within bacteriophage heads that is consistent with a wide range of biophysical data. Here we propose that bacteriophage DNA is packaged in a toroid that is folded into a highly compact structure.
    Biophysical Journal 11/1995; 69(4):1355-62. DOI:10.1016/S0006-3495(95)80002-0 · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Poly[2-(dimethylamino)ethyl methacrylate-b-2-methacryloyloxyethyl phosphorylcholine] (DMA-MPC) is currently under investigation as a new vector candidate for gene therapy. The DMA block has been previously demonstrated to condense DNA effectively. The MPC block contains a phosphorylcholine (PC) headgroup, which can be found naturally in the outside of the cell membrane. This PC-based polymer is extremely hydrophilic and acts as a biocompatible steric stabilizer. In this study, we assess in detail the morphologies of DNA complexes obtained using the diblock copolymer series DMA(x)MPC30 (where the mean degree of polymerization of the MPC block was fixed at 30 and the DMA block length was systematically varied) using transmission electron microscopy (TEM) and liquid atomic force microscopy (AFM). Both techniques indicate more compact complex morphologies (more efficient condensation) as the length of the cationic DMA block increases. However, the detailed morphologies of the DMA(x)MPC30-DNA complexes observed by TEM in vacuo and by AFM in aqueous medium are different. This phenomena is believed to be related to the highly hydrophilic nature of the MPC block. TEM studies revealed that the morphology of the complexes changes from loosely condensed structures to highly condensed rods, toroids, and oval-shaped particles as the DMA moiety increases. In contrast, morphological changes from plectonemic loops to flower-like and rectangular block-like structures, with an increase in highly condensed central regions, are observed by in situ AFM studies. The relative population of each structure is clearly dependent on the polymer molecular composition. Enzymatic degradation assays revealed that only the DMA homopolymer provided effective DNA protection against DNase I degradation, while other highly condensed copolymer complexes, as judged from TEM and gel electrophoresis, only partially protected the DNA. However, AFM images indicated that the same highly condensed complexes have less condensed regions, which we believe to be the initiation sites for enzymatic attack. This indicates that the open structures observed by AFM of the DNA complexation by the DMA(x)MPC30 copolymer series are closer to in vivo morphology when compared to TEM.
    Langmuir 05/2005; 21(8):3591-8. DOI:10.1021/la047480i · 4.38 Impact Factor