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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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The behavior of the yaw (Φ) angle in CU in response to forces applied at PU and/or the addition of neighboring units. (a) Φ in CU when the network grows from 1 ring (R1) to 10 rings (R10). Each network is subjected to increasing forces sequentially from 2.5 to 25 pN; an extra ring of PU is added to the existing network and the same range of forces is applied again. Φ remains relatively constant within the range of radial forces (e.g., within R5), but jumps each time an additional ring is added (e.g., from R1 to R2). (b) Diagram following one example of protofilament, where its Φ jumps from one of the preferred six angles to another preferred angles when each ring is added. A single unit is shown with Φ = 30°
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Fig6: The behavior of the yaw (Φ) angle in CU in response to forces applied at PU and/or the addition of neighboring units. (a) Φ in CU when the network grows from 1 ring (R1) to 10 rings (R10). Each network is subjected to increasing forces sequentially from 2.5 to 25 pN; an extra ring of PU is added to the existing network and the same range of forces is applied again. Φ remains relatively constant within the range of radial forces (e.g., within R5), but jumps each time an additional ring is added (e.g., from R1 to R2). (b) Diagram following one example of protofilament, where its Φ jumps from one of the preferred six angles to another preferred angles when each ring is added. A single unit is shown with Φ = 30°

Mentions: Increasing force applied to the networks from 5.0 to 25 pN did not alter Φ of the CU significantly (e.g., see R5 in Fig. 6a). However, addition of rings (Fig. 4), drastically changed Φ to a new value (e.g., from R6 to R7 in Fig. 6a). Such change may be attributed to the random inter-unit connectivity with several new PU, indicating the drastic influence exerted by the neighboring units. These predictions imply that the inter-unit connectivity may dominate the Φ values of the actin protofilaments in each unit, especially during the construction phase of the skeletal network. Once connections are made and the network is completed; however, the Φ values may be largely maintained. Since the yaw angle distributions in networks of 5, 7, and 10 rings are similar, consistent behaviors may be expected in larger networks consisting of more than 100 rings as found in whole erythrocytes.FIGURE 6


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)

The behavior of the yaw (Φ) angle in CU in response to forces applied at PU and/or the addition of neighboring units. (a) Φ in CU when the network grows from 1 ring (R1) to 10 rings (R10). Each network is subjected to increasing forces sequentially from 2.5 to 25 pN; an extra ring of PU is added to the existing network and the same range of forces is applied again. Φ remains relatively constant within the range of radial forces (e.g., within R5), but jumps each time an additional ring is added (e.g., from R1 to R2). (b) Diagram following one example of protofilament, where its Φ jumps from one of the preferred six angles to another preferred angles when each ring is added. A single unit is shown with Φ = 30°
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Related In: Results  -  Collection

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Fig6: The behavior of the yaw (Φ) angle in CU in response to forces applied at PU and/or the addition of neighboring units. (a) Φ in CU when the network grows from 1 ring (R1) to 10 rings (R10). Each network is subjected to increasing forces sequentially from 2.5 to 25 pN; an extra ring of PU is added to the existing network and the same range of forces is applied again. Φ remains relatively constant within the range of radial forces (e.g., within R5), but jumps each time an additional ring is added (e.g., from R1 to R2). (b) Diagram following one example of protofilament, where its Φ jumps from one of the preferred six angles to another preferred angles when each ring is added. A single unit is shown with Φ = 30°
Mentions: Increasing force applied to the networks from 5.0 to 25 pN did not alter Φ of the CU significantly (e.g., see R5 in Fig. 6a). However, addition of rings (Fig. 4), drastically changed Φ to a new value (e.g., from R6 to R7 in Fig. 6a). Such change may be attributed to the random inter-unit connectivity with several new PU, indicating the drastic influence exerted by the neighboring units. These predictions imply that the inter-unit connectivity may dominate the Φ values of the actin protofilaments in each unit, especially during the construction phase of the skeletal network. Once connections are made and the network is completed; however, the Φ values may be largely maintained. Since the yaw angle distributions in networks of 5, 7, and 10 rings are similar, consistent behaviors may be expected in larger networks consisting of more than 100 rings as found in whole erythrocytes.FIGURE 6

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