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Scholarly Works (3 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2003)

It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are uniformly similar to37 nm and the membrane skeleton consists of hexagons. We have previously proposed that a "molecular ruler" formed by E-tropomodulin and tropomyosin 5 or 5b functions to generate protofilaments of 12 G actin under mechanical stress. Here, we illustrate that intrinsic properties of actin filaments, e.g., turns, chemical bonds, and dimensions of the helix, also favor fragmentation into protofilaments under mechanical stress. We further construct a mechanical model in that a pair of G actin is wrapped around by a split alphaand beta spectrin, which may spin to two potential positions, and stabilize to one when the tail end is restricted. A reinforced protofilament may function as a mechanical axis to anchor three (top, middle, and bottom) pairs of Sp. Each Sp pair may wrap around the protofilament with a wide dihedral angle (similar to166.2degrees) and a minimal axial distance (2.75 nm). Such three Sp pairs may spiral down (right handed) the protofilament from the pointed end with a dihedral angle of similar to55.4degrees in between the Sp pairs. This first three-dimensional model of JC may explain the hexagonal geometry of the erythrocyte membrane skeleton. (C) 2003 Biomedical Engineering Society. The original publication is available at www.springerlink.com.

    Cover page: Protofilament and hexagon: A three-dimensional mechanical model for the junctional complex in the erythrocyte membrane skeleton
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2010)
    Erythrocytes undergo deformations when they transport O2 and CO2 across the membrane, yet the 3D nanomechanics of the skeletal network remains poorly understood. Expanding from our previous single isolated unit, we now simulate networks consisting of 1–10 concentric rings of repeating units in equibiaxial deformation. The networks are organized with (1) a 3D model for a single unit, (2) a wrap-around mode between Sp and actin protofilament in the intra-unit interaction, and (3) a random inter-unit connectivity. These assumptions permit efficient five-degrees-of-freedom (5DOF) simulations when up to 30 pN of radial forces are applied to the boundary spectrin (Sp) and the center and other units are analyzed. As 6 Sp balance their tensions, hexagonal units become irregular. While actin protofilaments remain tangent to the network, their yaw (Φ) angles change drastically with addition of neighboring units or an Sp unfolding. It is anticipated that during deformation, transmembrane complexes associated with the network move laterally through the lipid bilayer and increase the diffusion of molecules across the membrane. When protofilament/Sp sweeps under the lipid bilayer, they mix up the submembrane concentration gradient. Thus, the nanomechanics of actin protofilaments and Sp may enhance the transport of molecules during erythrocyte deformation.
      Cover page: Nanomechanics of Multiple Units in the Erythrocyte Membrane Skeletal Network
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2014)
      The physiological functions of erythrocytes depend critically on their morphology, deformability, and aggregation capability in response to external physical and chemical stimuli. The dynamic deformability can be described in terms of their viscoelasticity. We applied jumping optical tweezers to trap and stretch individual red blood cells (RBCs) to characterize its viscoelasticity in terms of the Young's modulus and viscosity by analyzing the experimental data of dynamic deformation using a 2-parameter Kelvin solid model. The effects of three chemical agents (N -ethylmaleimide, Chymotrypsin, and Hydrogen peroxide) on RBC's mechanical properties were studied by comparing the Young's modulus and viscosity of RBCs with and without these chemical treatments. Although the effects of each of these chemicals on the molecular structures of RBC may not be exclusive, based on the dominant effect of each chemical, we attempted to dissect the main contributions of different constituents of the RBC membrane to its viscosity and elasticity. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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