3-D Nanomechanics of an Erythrocyte Junctional Complex in Equibiaxial and Anisotropic Deformations

Abstract

The erythrocyte membrane skeleton deforms constantly in circulation, but the mechanics of a junctional complex (JC) in the network is poorly understood. We previously proposed a 3-D mechanical model for a JC (Sung, L. A., and C. Vera. Protofilament and hexagon: A three-dimensional mechanical model for the junctional complex in the erythrocyte membrane skeleton. Ann Biomed Eng 31:1314–1326, 2003) and now developed a mathematical model to compute its equilibrium by dynamic relaxation. We simulated deformations of a single unit in the network to predict the tension of 6 αβ spectrin (Sp) (top, middle, and bottom pairs), and the attitude of the actin protofilament [pitch (θ), yaw (φ) and roll (ψ) angles]. In equibiaxial deformation, 6 Sp would not begin their first round of “single domain unfolding in cluster” until the extension ratio (λ) reach ~3.6, beyond the maximal sustainable λ of ~2.67. Before Sp unfolds, the protofilament would gradually raise its pointed end away from the membrane, while φ and ψ remain almost unchanged. In anisotropic deformation, protofilaments would remain tangent but swing and roll drastically at least once between λ _i = 1.0 and ~2.8, in a deformation angle- and λ _i -dependent fashion. This newly predicted nanomechanics in response to deformations may reveal functional roles previous unseen for a JC, and molecules associated with it, during erythrocyte circulation.