title: Intertwined αβ spectrin meeting helical actin protofilament in the erythrocyte membrane skeleton: wrap-around vs. point-attachment.
abstract: Our 3-D model for a junctional complex (JC) in the erythrocyte membrane skeleton proposed that the helical actin protofilament functions as a mechanical axis for three pairs of αβ spectrin (Sp), and each pair wraps around the protofilament in a back-to-back fashion. The distal end of each Sp is further associated with the lipid bilayer by a suspension complex (SC). Here, we detail how splitting and rejoining of αβ Sp around a protofilament may form a loop that sustains and equilibrates tension. Sequential association of β and α Sp solves the challenge of constructing multiple loops along the protofilament, and topological connection facilitates their re-association. The wrap-around model minimizes the strain of the actin binding site on β Sp due to tension, redirection, or sliding of intertwined Sp. Pairing Sp balances the opposing forces and provides a mechanism for elastic recovery. The wrap-around junction thus provides mechanical advantages over a point-attachment junction in maintaining the integrity and functionality of the network. Severing α or β Sp may convert a wrapping-around junction to a point-attachment junction. In that case, a "bow up" motion of JC during deformation may disturb or flip the overlaid lipid bilayer, and mark stressed erythrocytes for phagocytosis.
authors.affiliation: Department of Bioengineering, Jacobs School of Engineering, University of California, La Jolla, San Diego, CA 92093-0412, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Sche
authors.forename: Carlos
authors.initials: C
authors.lastname: Vera
authors.forename: L Amy
authors.initials: LA
authors.lastname: Sung
mesh_terms: D001665:Binding Sites; D003094:Collagen / Q000737:chemistry* / Q000648:ultrastructure*; D003198:Computer Simulation; D004910:Erythrocyte Membrane / Q000737:chemistry* / Q000648:ultrastructure*; D008955:Models, Cardiovascular; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D013049:Spectrin / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D013049:Spectrin; D003094:Collagen