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Nanomechanics of multiple units in the erythrocyte membrane skeletal network.

de Oliveira M, Vera C, Valdez P, Sharma Y, Skelton R, Sung LA - Ann Biomed Eng (2010)

Bottom Line: While actin protofilaments remain tangent to the network, their yaw (Phi) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, 92093, USA.

ABSTRACT
Erythrocytes undergo deformations when they transport O(2) and CO(2) 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 (Phi) 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.

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Six preferential Φ angles of JC in the network. (a) Histogram of Φ angles in all units or CU from 1500 simulations. Six preferred Φ angles (−150°, −90°, −30°, 30°, 90°, and 150°) in the networks of various size are present when a step 2.5 pN was sequentially applied. (b) A 5-ring network simulation after 5 pN was applied. Note the orientation of protofilament in all units. (c) Histogram of Φ angles from all units, showing the variation from the mean value of preferred angles (the vertical axis is in thousands)
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Fig7: Six preferential Φ angles of JC in the network. (a) Histogram of Φ angles in all units or CU from 1500 simulations. Six preferred Φ angles (−150°, −90°, −30°, 30°, 90°, and 150°) in the networks of various size are present when a step 2.5 pN was sequentially applied. (b) A 5-ring network simulation after 5 pN was applied. Note the orientation of protofilament in all units. (c) Histogram of Φ angles from all units, showing the variation from the mean value of preferred angles (the vertical axis is in thousands)

Mentions: However, there seemed to be six preferred Φ values with an interval of ~60°. This was not only found in CU, but also in all units. For example, Fig. 7a shows a histogram of Φ in 1500 simulations and six preferred Φ values of about −150°, −90°, −30°, 30°, 90°, and 150° were predicted. This is surprising considering the number of units involved in the networks (e.g., 271 units in 10 rings, Fig. 7b). Remarkably, as a ring of units was added, Φ of CU drastically changed from one to another preferred angle (Fig. 6b).FIGURE 7


Nanomechanics of multiple units in the erythrocyte membrane skeletal network.

de Oliveira M, Vera C, Valdez P, Sharma Y, Skelton R, Sung LA - Ann Biomed Eng (2010)

Six preferential Φ angles of JC in the network. (a) Histogram of Φ angles in all units or CU from 1500 simulations. Six preferred Φ angles (−150°, −90°, −30°, 30°, 90°, and 150°) in the networks of various size are present when a step 2.5 pN was sequentially applied. (b) A 5-ring network simulation after 5 pN was applied. Note the orientation of protofilament in all units. (c) Histogram of Φ angles from all units, showing the variation from the mean value of preferred angles (the vertical axis is in thousands)
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2914261&req=5

Fig7: Six preferential Φ angles of JC in the network. (a) Histogram of Φ angles in all units or CU from 1500 simulations. Six preferred Φ angles (−150°, −90°, −30°, 30°, 90°, and 150°) in the networks of various size are present when a step 2.5 pN was sequentially applied. (b) A 5-ring network simulation after 5 pN was applied. Note the orientation of protofilament in all units. (c) Histogram of Φ angles from all units, showing the variation from the mean value of preferred angles (the vertical axis is in thousands)
Mentions: However, there seemed to be six preferred Φ values with an interval of ~60°. This was not only found in CU, but also in all units. For example, Fig. 7a shows a histogram of Φ in 1500 simulations and six preferred Φ values of about −150°, −90°, −30°, 30°, 90°, and 150° were predicted. This is surprising considering the number of units involved in the networks (e.g., 271 units in 10 rings, Fig. 7b). Remarkably, as a ring of units was added, Φ of CU drastically changed from one to another preferred angle (Fig. 6b).FIGURE 7

Bottom Line: While actin protofilaments remain tangent to the network, their yaw (Phi) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, 92093, USA.

ABSTRACT
Erythrocytes undergo deformations when they transport O(2) and CO(2) 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 (Phi) 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.

Show MeSH
Related in: MedlinePlus