Structure of the alpha-actinin rod: molecular basis for cross-linking of actin filaments.

Structural Biology Programme, European Molecular Biology Laboratory, Heidelberg, Germany.
Cell (Impact Factor: 32.24). 09/1999; 98(4):537-46.
Source: PubMed


We have determined the crystal structure of the two central repeats in the alpha-actinin rod at 2.5 A resolution. The repeats are connected by a helical linker and form a symmetric, antiparallel dimer in which the repeats are aligned rather than staggered. Using this structure, which reveals the structural principle that governs the architecture of alpha-actinin, we have devised a plausible model of the entire alpha-actinin rod. The electrostatic properties explain how the two alpha-actinin subunits assemble in an antiparallel fashion, placing the actin-binding sites at both ends of the rod. This molecular architecture results in a protein that is able to form cross-links between actin filaments.

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Available from: Kristina Djinović-Carugo, Dec 15, 2014
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    • "Actin filament bundling by α-actinin is implicated in a variety of cellular structures such as stress fibers, adhesions, junctions, and dendritic spines [7], [8]. α-Actinin is an antiparallel homodimer with an actin-binding site on either end that mediates actin filament cross-linking [9]. The N-terminal actin binding domain is followed by four tandem spectrin repeats and a calmodulin-like domain, that determines each isoform's calcium sensitivity, at its C-terminus [10]–[12]. "
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    ABSTRACT: Dendritic spines are micron-sized protrusions that constitute the primary post-synaptic sites of excitatory neurotransmission in the brain. Spines mature from a filopodia-like protrusion into a mushroom-shaped morphology with a post-synaptic density (PSD) at its tip. Modulation of the actin cytoskeleton drives these morphological changes as well as the spine dynamics that underlie learning and memory. Several PSD molecules respond to glutamate receptor activation and relay signals to the underlying actin cytoskeleton to regulate the structural changes in spine and PSD morphology. α-Actinin-2 is an actin filament cross-linker, which localizes to dendritic spines, enriched within the post-synaptic density, and implicated in actin organization. We show that loss of α-actinin-2 in rat hippocampal neurons creates an increased density of immature, filopodia-like protrusions that fail to mature into a mushroom-shaped spine during development. α-Actinin-2 knockdown also prevents the recruitment and stabilization of the PSD in the spine, resulting in failure of synapse formation, and an inability to structurally respond to chemical stimulation of the N-methyl-D-aspartate (NMDA)-type glutamate receptor. The Ca2+-insensitive EF-hand motif in α-actinin-2 is necessary for the molecule's function in regulating spine morphology and PSD assembly, since exchanging it for the similar but Ca2+-sensitive domain from α-actinin-4, another α-actinin isoform, inhibits its function. Furthermore, when the Ca2+-insensitive domain from α-actinin-2 is inserted into α-actinin-4 and expressed in neurons, it creates mature spines. These observations support a model whereby α-actinin-2, partially through its Ca2+-insensitive EF-hand motif, nucleates PSD formation via F-actin organization and modulates spine maturation to mediate synaptogenesis.
    PLoS ONE 07/2014; 9(7):e101770. DOI:10.1371/journal.pone.0101770 · 3.23 Impact Factor
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    • "Although most SR proteins contain CHDs, some possess motifs which can interact with other cytoskeletal components, allowing linkage of SR-associated complexes to filamentous structures other than F-actin. In addition, these motifs allow cross-linking between different filaments and dynamic re-modelling of the cells internal framework in response to altered mechanical needs (Refs 5, 6, 7). The SR family is composed of a growing list of proteins that include α-actinins, α/β-spectrins, dystrophins and spectraplakins. "
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    ABSTRACT: Nuclear envelope spectrin-repeat proteins (Nesprins), are a novel family of nuclear and cytoskeletal proteins with rapidly expanding roles as intracellular scaffolds and linkers. Originally described as proteins that localise to the nuclear envelope (NE) and establish nuclear-cytoskeletal connections, nesprins have now been found to comprise a diverse spectrum of tissue specific isoforms that localise to multiple sub-cellular compartments. Here, we describe how nesprins are necessary in maintaining cellular architecture by acting as essential scaffolds and linkers at both the NE and other sub-cellular domains. More importantly, we speculate how nesprin mutations may disrupt tissue specific nesprin scaffolds and explain the tissue specific nature of many nesprin-associated diseases, including laminopathies.
    Expert Reviews in Molecular Medicine 03/2013; 15:e5. DOI:10.1017/erm.2013.6 · 5.15 Impact Factor
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    • "Spectrin repeat structures from α/β−spectrin [31], [32], [33], [34], [35], α-actinin [36], [37] and plakins [38], [39], [40] have a three-helix (A–B–C) bundle fold with the multiple repeat structures showing that the C helix of the preceding repeat is continuous with the A’ helix of the next. The structural nature of this connecting linker between repeats has important implications for the biophysical characteristics of the whole rod region [41]. "
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    ABSTRACT: Dystrophin and utrophin link the F-actin cytoskeleton to the cell membrane via an associated glycoprotein complex. This functionality results from their domain organization having an N-terminal actin-binding domain followed by multiple spectrin-repeat domains and then C-terminal protein-binding motifs. Therapeutic strategies to replace defective dystrophin with utrophin in patients with Duchenne muscular dystrophy require full-characterization of both these proteins to assess their degree of structural and functional equivalence. Here the high resolution structures of the first spectrin repeats (N-terminal repeat 1) from both dystrophin and utrophin have been determined by x-ray crystallography. The repeat structures both display a three-helix bundle fold very similar to one another and to homologous domains from spectrin, α-actinin and plectin. The utrophin and dystrophin repeat structures reveal the relationship between the structural domain and the canonical spectrin repeat domain sequence motif, showing the compact structural domain of spectrin repeat one to be extended at the C-terminus relative to its previously defined sequence repeat. These structures explain previous in vitro biochemical studies in which extending dystrophin spectrin repeat domain length leads to increased protein stability. Furthermore we show that the first dystrophin and utrophin spectrin repeats have no affinity for F-actin in the absence of other domains.
    PLoS ONE 07/2012; 7(7):e40066. DOI:10.1371/journal.pone.0040066 · 3.23 Impact Factor
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