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Reversible swelling of SBMV is associated with reversible disordering.

ABSTRACT: The structures of the compact and swollen southern bean mosaic virus (SBMV) particles have been compared by X-ray diffraction and proton magnetic resonance (PMR). Small-angle X-ray scattering showed that removal of divalent cations at alkaline pH causes the particle diameter to increase from 289Å in the native SBMV by 12% in solution and by 9% in microcrystals. The swelling is fully reversible upon re-addition of Ca2+ and Mg2+ ions, as shown by the X-ray patterns at 6Å resolution and by the 270MHz PMR spectra. Beyond 30Å resolution, X-ray patterns from the compact SBMV in solution and in microcrystals show fine fringes of ?1/225Å-1 width extending to 6Å resolution, whereas patterns from the swollen SBMV in solution and in microcrystals show only broader fringes of ?1/90Å-1 width, Model calculations demonstrate that the fine fringes from compact SBMV arise from regular packing of the protein subunits on the icosahedral surface lattice; the smearing of fine fringes in the swollen virus pattern can be simulated by uncorrelated displacements of pentamers and hexamers of protein subunits, with a standard deviation of 6Å from their mean locations. The PMR spectrum of compact SBMV is poorly resolved, whereas PMR spectrum of swollen SBMV shows sharp resonances in the methyl proton region. The line-narrowing for a fraction of the aliphatic protons upon swelling cannot be accounted for by rotational relaxation of the particle of 6×106MW, but must be attributed to internal motion in small regions of the protein subunits.

SUBMITTER: Li J

PROVIDER: S-EPMC5784231 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Reversible swelling of SBMV is associated with reversible disordering.

Li Jade J Fricks Carl C Rayment Ivan I Caspar Donald L D DLD

Journal of structural biology 20170621 3

The structures of the compact and swollen southern bean mosaic virus (SBMV) particles have been compared by X-ray diffraction and proton magnetic resonance (PMR). Small-angle X-ray scattering showed that removal of divalent cations at alkaline pH causes the particle diameter to increase from 289Å in the native SBMV by 12% in solution and by 9% in microcrystals. The swelling is fully reversible upon re-addition of Ca<sup>2+</sup> and Mg<sup>2+</sup> ions, as shown by the X-ray patterns at 6Å reso ...[more]

PMID: 28647540

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Project description:This study investigates the swelling of grafted polycationic brushes as a function of pH and anion type. The brushes are chitosan (CH) and chitosans with 27% and 51% degree of substitution (DS) of quaternary ammonium salt, denoted as CH-Q(25) and CH-Q(50), respectively. The water content and swelling behaviors are monitored using in situ quartz-crystal microbalance with dissipation (QCM-D). The pH varies from ~3.5 to 8.5, and the counter anion types include chloride, acetate, and citrate. At fixed pH, the water content and brush swelling increase as the DS increases. Whereas the CH-Q(50) brush layer shows symmetric swelling with a minimum near pH = 4.5, the swelling of CH and CH-Q(25) is relatively constant as pH decreases from 8.2 to 5.5, and then begins to increase near pH 4. These studies indicate that the symmetric swelling of CH-Q(50) is likely attributed to increasing protonation of primary amines for pH values below pH 6.5 and the quaternary ammonium salts above pH 6.5. At pH 4, the swelling of the CH brush increases upon exchanging the smaller chloridewith a bulkier acetate anion, which is less effective at screening intra/inter molecular repulsion. In contrast, upon exchanging the acetate with trifunctional citrate, CH and CH-Q(25) brushes collapse by 53 and 42%, respectively, because the citrate forms ionic cross-links. To test antibacterial properties, silicon oxide, CH and CH-Q(50) brush layers are exposed to 10(7)-10(8) cfu/ml of S. aureus for two days at 37 °C and exposed to stepped shear stresses in 2 min intervals. Whereas an S. aureus biofilm adheres strongly to silicon oxide and CH for stresses up to 12 dyne/cm(2), biofilms on CH-Q(50) detach at a relatively low shear stress, 1.5 dyne/cm(2). Due to their high degree of swelling that can be tuned via pH, counterion size and type, chitosan and quaternary modified chitosans have potential as responsive coatings for applications including MEMS/NEMS devices and drug eluting implants.

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Reversible swelling of SBMV is associated with reversible disordering.

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Reversible swelling of SBMV is associated with reversible disordering.

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