An Ankyrin-Based Mechanism for Functional Organization of Dystrophin and Dystroglycan

Abstract

beta-dystroglycan (DG) and the dystrophin-glycoprotein complex (DGC) are localized at costameres and neuromuscular junctions in the sarcolemma of skeletal muscle. We present evidence for an ankyrin-based mechanism for sarcolemmal localization of dystrophin and beta-DG. Dystrophin binds ankyrin-B and ankyrin-G, while beta-DG binds ankyrin-G. Dystrophin and beta-DG require ankyrin-G for retention at costameres but not delivery to the sarcolemma. Dystrophin and beta-DG remain intracellular in ankyrin-B-depleted muscle, where beta-DG accumulates in a juxta-TGN compartment. The neuromuscular junction requires ankyrin-B for localization of dystrophin/utrophin and beta-DG and for maintenance of its postnatal morphology. A Becker muscular dystrophy mutation reduces ankyrin binding and impairs sarcolemmal localization of dystrophin-Dp71. Ankyrin-B also binds to dynactin-4, a dynactin subunit. Dynactin-4 and a subset of microtubules disappear from sarcolemmal sites in ankyrin-B-depleted muscle. Ankyrin-B thus is an adaptor required for sarcolemmal localization of dystrophin, as well as dynactin-4.

Microtubule binding distinguishes dystrophin from utrophin

“…However, the cosedimentation assay used previously (19) was performed on skeletal muscle lysates from mice expressing endogenous dystrophin or transgenic dystrophin constructs, which cannot distinguish between direct and indirect interactions, and dystrophin also interacts with microtubules via ankyrin-B (16,59). Here, using purified recombinant dystrophin proteins and tubulin in a high-speed cosedimentation assay, we identified spectrin-like repeats 20-23 in the direct binding interaction of dystrophin with microtubules.…”

“…Although the mdx mouse expresses increased utrophin, these levels fail to restore nNOS to the sarcolemma or rescue the disorganized microtubule lattice that results owing to loss of dystrophin (16,19,34,35), indicating that utrophin cannot fully compensate for the lack of dystrophin. There are two main possibilities why endogenously up-regulated utrophin fails to retain microtubule lattice organization.…”

“…Through its many protein interactions, dystrophin is hypothesized to protect against contraction-induced muscle damage via radial force transmission and stabilization of the sarcolemma (13)(14)(15). Additionally, through both direct and indirect interactions via proteins such as ankyrin-B and obscurin, dystrophin has been found to bind microtubules to form a rectilinear lattice beneath the sarcolemma (16)(17)(18)(19)(20).…”

eDystrophin : un nouvel outil dédié à une meilleure compréhension des dystrophinopathies

“…Le domaine CRR se lie avec le β-dystroglycane (β-DG) qui, en interagissant avec l'α-dystroglycane et les sarcoglycanes, forme le complexe dystrophine-glycoprotéines (DGC) [5,9]. Il se lie aussi à la syné-mine α [4], la plectine [31], la myosprine (protéine kinase de type A) [29] et l'ankyrine [3].…”

Spectrin mutations that cause spinocerebellar ataxia type 5 impair axonal transport and induce neurodegeneration inDrosophila

“…Although the protein interactions that mediate synapse stability are not fully understood, one model is that synaptic components at the membrane are stabilized through spectrin and ankyrin linkages to the cytoskeleton (Pielage et al, 2006(Pielage et al, , 2008Ayalon et al, 2008;Koch et al, 2008), and that the establishment of these connections is facilitated by dynein/dynactin recruitment of microtubules (Carminati and Stearns, 1997;Adames and Cooper, 2000;Ligon et al, 2001;Schuyler and Pellman, 2001;Dujardin and Vallee, 2002). The binding of ankyrin to the p62 subunit of dynactin, as well as the reported binding of ankyrin to microtubules, supports the hypothesis that spectrin and ankyrin may act together to stabilize the synaptic membrane through the dynactin/dyneinmediated capture of microtubules (Ayalon et al, 2008;Koch et al, 2008;Pielage et al, 2008). Consistent with this model, synapse disassembly has also been reported after disruption of dynactin function (Eaton et al, 2002).…”