Fiber Rigidity Research Articles

Flexibility of the adenovirus fiber is required for efficient receptor interaction.

The adenovirus (Ad) fiber protein mediates Ad binding to the coxsackievirus and Ad receptor (CAR) and is thus a major determinant of viral tropism. The fiber contains three domains: an N-terminal tail that anchors the fiber to the viral capsid, a central shaft region of variable length and flexibility, and a C-terminal knob domain that binds to cell receptors. Ad type 37 (Ad37), a subgroup D virus associated with severe ocular infections, is unable to use CAR efficiently to infect host cells, despite containing a CAR binding site in its fiber knob. We hypothesized that the relatively short, inflexible Ad37 fiber protein restricts interactions with CAR at the cell surface. To test this hypothesis, we analyzed the infectivity and binding of recombinant Ad particles containing modified Ad37 or Ad5 fiber proteins. Ad5 particles equipped with a truncated Ad5 fiber or with a chimeric fiber protein comprised of the Ad5 knob fused to the short, rigid Ad37 shaft domain had significantly reduced infectivity and attachment. In contrast, placing the Ad37 knob onto the long, flexible Ad5 shaft allowed CAR-dependent virus infection and cell attachment, demonstrating the importance of the shaft domain in receptor usage. Increasing fiber rigidity by substituting the predicted flexibility modules in the Ad5 shaft with the corresponding regions of the rigid Ad37 fiber dramatically reduced both virus infection and cell attachment. Cryoelectron microscopy (cryo-EM) single-particle analysis demonstrated the increased rigidity of this chimeric fiber. These studies demonstrate that both length and flexibility of the fiber shaft regulate CAR interaction and provide a molecular explanation for the use of alternative receptors by subgroup D Ad with ocular tropism. We present a molecular model for Ad-CAR interactions at the cell surface that explains the significance of fiber flexibility in cell attachment.

Structural analysis of a fiber-pseudotyped adenovirus with ocular tropism suggests differential modes of cell receptor interactions.

Adenovirus (Ad) entry into cells is initiated by the binding of the fiber knob to a cell surface receptor. The coxsackie- and adenovirus receptor (CAR) functions as the attachment receptor for many, but not all, Ad serotypes. Ad type 37 (Ad37), a subgroup D virus that causes keratoconjunctivitis in humans, does not infect cells via CAR despite demonstrated binding of the Ad37 knob to CAR. We have pseudotyped a fiber deletion Ad5 vector with the Ad37 fiber (Ad37f), and this vector retains the ocular tropism of Ad37. Here we present a cryo-electron microscopy reconstruction of Ad37f that shows the entire Ad37 fiber, including the shaft and knob domains. We have previously proposed that Ad37 may not utilize CAR for cell entry because of the geometric constraints imposed by a rigid fiber (E. Wu, J. Fernandez, S. K. Fleck, D. Von Seggern, S. Huang, and G. R. Nemerow, Virology 279:78-89, 2001). Consistent with this hypothesis, our structural results show that the Ad37 fiber is straight and rigid. Modeling of the interaction between Ad37f and host cell receptors indicates that fiber flexibility or rigidity, as well as length, can affect receptor usage and cellular tropism.

Poly(vinyl chloride) Thermoreversible Gels: A Fractal Approach to the Relation between Structure and Mechanical Properties

Poly(vinyl chloride) aggregates have been studied by static light scattering in diesters and monoesters. By considering a fibrillar structure, it has been assumed that these experiments provide one with the longitudinal fractal dimension of the fibers, which equals Df = 1.5 ± 0.1 independent of the solvent type. Relations established between the elastic modulus and the polymer concentration for the same solvents have been accounted for in most cases by using both a theory developed by Jones and Marques for rigid networks and the fractal dimension as deduced from light scattering. The mechanisms promoting fiber rigidity in these gels are discussed.

Dynamic rheological studies of hydrophobic interactions in injectable collagen biomaterials

AbstractInjectable collagen is a concentrated dispersion of collagen fibers in aqueous solution that is used to correct dermal contour defects through intradermal injection. The effect of hydrophobic forces on the rheology of concentrated dispersions of collagen fibers was studied by dynamic rheological measurements over temperatures ranging from 283 to 308 K. The results are interpreted in terms of the associated relaxation time spectra and the theory of Kamphuis et al. for concentrated dispersions. Increases in fiber rigidity are seen from a progressive decrease in the slope of the linear log G′ (or G″) vs. log ω data recorded for these dispersions as temperature is increased. A molecular interpretation of this result was obtained by treating collagen fibers as a liquid crystalline phase of rigid‐rod collagen molecules that have phase‐separated from aqueous solution. Hydrophobic forces affect the volume fraction of water that is present in the phase‐separated fibers, which, in turn, affects the rigidity of the fibers. Distinct yielding behavior (in the nonlinear viscoelastic region) occurs at temperatures above 293 K and reflects a gel transition. Thermal gelation of collagen dispersions is proposed to proceed through hydrophobically driven mechanisms of increased fiber rigidity and enhanced interfiber attractive forces. © 1993 John Wiley & Sons, Inc.

Holding Length: Effect on Digital Fibrograph Span Length

Fibers scanned for length by most instruments must be held in position for the scan. The holding length has been determined mathematically as being of the order of 4.06 mm ( 0.16 in.). Since the start of scan begins at 3.81 mm (0.15 in.) from the holding edge, the average start of scan actually begins at a length of 7.87 mm (0.31 in.). A general holding length is shown with a photomicrograph. Applying this concept to data presented in the literature gives acceptable results in all but one case. The holding length appears to be a function of fiber rigidity, which means that it varies.