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  • 1.
    Addario, Barbara
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Alpha-actinin of Schizosaccharomyces pombeManuskript (preprint) (Övrigt vetenskapligt)
  • 2.
    Addario, Barbara
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    The domain structure of Entamoeba α-actinin22010Ingår i: Cellular & Molecular Biology Letters (Druk), ISSN 1425-8153, E-ISSN 1689-1392, Vol. 15, nr 4, s. 665-78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Entamoeba histolytica, a major agent of human amoebiasis, expresses two distinct forms of α-actinin, a ubiquitous actin-binding protein that is present in most eukaryotic organisms. In contrast to all metazoan α-actinins, in both isoforms the intervening rod domain that connects the N-terminal actin-binding domain with the C-terminal EF-hands is much shorter. It is suggested that these α-actinins may be involved in amoeboid motility and phagocytosis, so we cloned and characterised each domain of one of these α-actinins to better understand their functional role. The results clearly showed that the domains have properties very similar to those of conventional α-actinins.

  • 3.
    Addario, Barbara
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Huang, Shenghua
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sauer, Uwe
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Crystallization and preliminary X-ray analysis of the Entamoeba histolytica α-actinin-2 rod domain2011Ingår i: Acta Crystallographica. Section F: Structural Biology and Crystallization Communications, ISSN 1744-3091, E-ISSN 1744-3091, Vol. 67, nr 10, s. 1214-1217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    -Actinins form antiparallel homodimers that are able to cross-link actin filaments. The protein contains three domains: an N-terminal actin-binding domain followed by a central rod domain and a calmodulin-like EF-hand domain at the C-terminus. Here, crystallization of the rod domain of Entamoeba histolytica -actinin-2 is reported; it crystallized in space group P212121, with unit-cell parameters a = 47.8, b = 79.1, c = 141.8 Å. A Matthews coefficient VM of 2.6 Å3 Da-1 suggests that there are two molecules and 52.5% solvent content in the asymmetric unit. A complete native data set extending to a d-spacing of 2.8 Å was collected on beamline I911-2 at MAX-lab, Sweden.

     

  • 4. Addario, Barbara
    et al.
    Sandblad, Linda
    Umeå universitet, Medicinska fakulteten, Institutionen för molekylärbiologi (Medicinska fakulteten).
    Persson, Karina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Characterisation of Schizosaccharomyces pombe alpha-actinin2016Ingår i: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 4, artikel-id e1858Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The actin cytoskeleton plays a fundamental role in eukaryotic cells. Its reorganization is regulated by a plethora of actin-modulating proteins, such as a-actinin. In higher organisms, alpha-actinin is characterized by the presence of three distinct structural domains: an N-terminal actin-binding domain and a C-terminal region with EF-hand motif separated by a central rod domain with four spectrin repeats. Sequence analysis has revealed that the central rod domain of alpha-actinin from the fission yeast Schizosaccharomyces pombe consists of only two spectrin repeats. To obtain a firmer understanding of the structure and function of this unconventional alpha-actinin, we have cloned and characterized each structural domain. Our results show that this alpha-actinin isoform is capable of forming dimers and that the rod domain is required for this. However, its actin-binding and cross-linking activity appears less efficient compared to conventional alpha-actinins. The solved crystal structure of the actin-binding domain indicates that the closed state is stabilised by hydrogen bonds and a salt bridge not present in other a-actinins, which may reduce the affinity for actin.

  • 5.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Alpha-actinin of the chlorarchiniophyte Bigelowiella natans2018Ingår i: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 6, artikel-id e4288Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The genome of the chlorarchiniophyte Bigelowiella natans codes for a protein annotated as an α-actinin-like protein. Analysis of the primary sequence indicate that this protein has the same domain structure as other α-actinins, a N-terminal actin-binding domain and a C-terminal calmodulin-like domain. These two domains are connected by a short rod domain, albeit long enough to form a single spectrin repeat. To analyse the functional properties of this protein, the full-length protein as well as the separate domains were cloned and isolated. Characerisation showed that the protein is capable of cross-linking actin filaments into dense bundles, probably due to dimer formation. Similar to human α-actinin, calcium-binding occurs to the most N-terminal EF-hand motif in the calmodulin-like C-terminal domain. The results indicate that this Bigelowiella protein is a proper α-actinin, with all common characteristics of a typical α-actinin.

  • 6.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Calcium affinity of human α-actinin12015Ingår i: PeerJ, Vol. 3, artikel-id e944Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to alternative splicing, the human ACTN1 gene codes for three different transcripts of α-actinin; one isoform that is expressed only in the brain and two with a more general expression pattern. The sequence difference is located to the C-terminal domains and the EF-hand motifs. Therefore, any functional or structural distinction should involve this part of the protein. To investigate this further, the calcium affinities of these three isoforms of α-actinin 1 have been determined by isothermal calorimetry.

  • 7.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Calmodulin—Alias: Cyclic Nucleotide Phosphodiesterase Activator, Ca2+-Dependent Regulatory Protein2007Ingår i: Calcium Binding Proteins, ISSN Print ISSN: 1554-8643; Online ISSN: 1554-8651, Vol. 2, nr 1, s. 1-3Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Calmodulin is an important intracellular receptor for calcium signals. Calcium-activated calmodulin interacts with a large number of targets, thereby transducing the signal to many cellular processes. Calmodulin is also the archetype for proteins binding calcium by the EF-hand motif.

  • 8.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Counter-current distribution of interacting molecules: simulation of distribution behaviour and application to protein-protein interactions1981Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Associations of biological macromolecules with other macromolecules, with larger assemblies of macromolecules and with themselves are widely encountered phenomena. In principle, these interactions can be studied with any method able to differentiate between free molecules and complexes formed. The most extensively used techniques are sedimentation equilibrium and velocity, elastic light scattering and molecular sieve chromatography. This thesis describes an alternative technique; counter-current distribution in aqueous two-phase systems.

    The counter-current distribution behaviour of a solute depends on its size and surface properties including charge and hydrophobicity. Since the surface properties of a complex formed most probably differ from those of the solutes participating in the association, complex formation should lead to changes in the average distribution behaviour of each solute. Consequently, the presence of one solute should affect the counter-current distribution of another solute if they interact with each other.

    In order to establish the boundary conditions and the potential as well as limitations of the counter-current distribution technique, the distribution behaviour of homogeneous and heterogeneous association equilibria have been simulated.

    The model developed for describing the distribution behaviour of heterogeneous associations has been tested using the well characterized interaction between bovine serum albumin and L-tryptophan. It was demonstrated that the theoretical model could predict the experimental distribution behaviour of these two molecules.

    However, the primary aim of the counter-current distribution experiments has been to gain insight into protein-protein interactions. The metabolically linked enzymes, malate dehydrogenase and aspartate aminotransferase, have been studied in order to determine if there is also a physical link between these two enzymes. The results showed that the cytosolic enzymes as well as the mitochondrial forms associate while the cytoplasmic enzymes did not display any association with the mitochondrial forms. Thus, an organelle specific interaction between malate dehydrogenase and aspartate aminotransferase was demonstrated.

    Hemoglobin and carbonic anhydrase are functionally linked through the Bohr effect. Thus, the binding of oxygen by hemoglobin in the lung capillaries is associated with the binding of protons which are formed by the catalytic action of carbonic anhydrase. From the counter- current distribution experiments it was possible to conclude that humain carbonic anhydrase II, the high activity form, associates with human hemoglobin whereas carbonic anhydrase I, the low activity form, did not show any affinity for hemoglobin.

  • 9.
    Backman, Lars
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Karina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    The no-nonsens SDS-PAGE2018Ingår i: Schizosaccharomyces pombe: methods and protocols / [ed] Teresa L. Singleton, Humana Press, 2018, s. 89-94Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    The discontinuous polyacrylamide gel electrophoresis system devised by Laemmli (Nature 227:680–685, 1970) has not only been used in numerous laboratories but has also been modified in several ways since its birth. In our laboratories, we use a modified Laemmli SDS-PAGE system for following protein purification as well as for analysis of certain protein-protein interactions, mainly involving filametous actin.

  • 10.
    Buevich, Alexei V
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lundberg, Susanne
    Sethson, Ingmar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Edlund, Ulf
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    NMR studies of calcium-binding to mutant alpha-spectrin EF-hands2004Ingår i: CELLULAR & MOLECULAR BIOLOGY LETTERS, ISSN 1425-8153, Vol. 9, nr 1, s. 167-86Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The co-operative calcium binding mechanism of the two C-terminal EF-hands of human all-spectrin has been investigated by site-specific mutagenesis and multi-dimensional NMR spectroscopy. To analyse the calcium binding of each EF-hand independently, two mutant structures (E33A and D69S) of wild type alpha-spectrin were prepared. According to NMR analysis both E33A and D69S were properly folded. The unmutated EF-hand in these mutants remained nearly intact and active in calcium binding, whereas the mutated EF-hand lost its affinity for calcium completely. The apparent calcium binding affinity of the E33A mutant was much lower compared to the D39S mutant (similar to2470 muM and similar to240 muM, respectively). When the chemical shift perturbations were followed upon calcium titration, a positive correlation between the D69S mutant and the binding of the first calcium ion to the wild type was revealed. These observations showed that the first EF-hand in spectrin binds the first calcium ion and thereby triggers a conformational change that allows the second calcium ion to bind to the other EF-hand.

  • 11.
    Karlsson, Göran
    et al.
    Swedish NMR Centre at the University of Gothenburg.
    Persson, Cecilia
    Swedish NMR Centre at the University of Gothenburg.
    Mayzel, Maxim
    Swedish NMR Centre at the University of Gothenburg.
    Hedenström, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Solution structure of the calmodulin-like C-terminal domain of Entamoeba α-actinin22016Ingår i: Proteins: Structure, Function, and Bioinformatics, ISSN 0887-3585, E-ISSN 1097-0134, Vol. 84, nr 4, s. 461-466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cell motility is dependent on a dynamic meshwork of actin filaments that is remodelled continuously. A large number of associated proteins that are severs, cross-links, or caps the filament ends have been identified and the actin cross-linker α-actinin has been implied in several important cellular processes. In Entamoeba histolytica, the etiological agent of human amoebiasis, α-actinin is believed to be required for infection. To better understand the role of α-actinin in the infectious process we have determined the solution structure of the C-terminal calmodulin-like domain using NMR. The final stru-ture ensemble of the apo form shows two lobes, that both resemble other pairs of calcium-binding EF-hand motifs, connected with a mobile linker.

  • 12. Löfvenberg, Lars
    et al.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    High-Performance Liquid Chromatography Analysis of Spectrin Oligomerization2001Ingår i: Analytical Biochemistry, Vol. 292, nr 2, s. 222-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gel filtration chromatography has been used to analyze the oligomerization of human erythrocyte spectrin. By applying an exponentially modified Gaussian function we have been able to resolve overlapping elution peaks. From these peaks it was possible to calculate the equilibrium composition of each spectrin concentration and thus also the dissociation constants describing the oligomeric process. The determined dissociation constants for tetramer formation (1.3 M) and for hexamer formation (24 M) agree well with other measurements.

  • 13.
    Persson, Karina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Crystallization of recombinant α-actinin and related proteins2018Ingår i: Schizosaccharomyces pombe: methods and protocols / [ed] Teresa L. Singleton, Humana Press, 2018, s. 95-103Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    When it comes to crystallization each protein is unique. It can never be predicted beforehand in which condition the particular protein will crystallize or even if it is possible to crystallize. Still, by following some simple checkpoints the chances of obtaining crystals are increased. The primary checkpoints are purity, stability, concentration, and homogeneity. High-quality protein crystals are needed. This protocol will allow an investigator to: clone, express, and crystallize a protein of interest.

  • 14.
    Petzold, Katja
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Öhman, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå centrum för molekylär patogenes (UCMP) (Teknisk-naturvetenskaplig fakultet).
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Folding of the αΙΙ-spectrin SH3 domain under physiological salt conditions2008Ingår i: Archives of Biochemistry and Biophysics, ISSN 0003-9861, E-ISSN 1096-0384, Vol. 474, nr 1, s. 39-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The SH3 domain has often been used as a model for protein folding due to its typical two-state behaviour. However, recent experimental data at low pH as well as molecular dynamic simulations have indicated that the folding process of SH3 probably is more complicated, and may involve intermediate states. Using both kinetic and equilibrium measurements we have obtained evidence that under native-like conditions the folding of the spectrin SH3 domain does not follow a classic two-state behaviour. The curvature we observed in the Chevron plots is a strong indication of a non-linear activation energy relationship due to the presence of high-energy intermediates. In addition, circular dichroism measurements indicated that refolding after thermal denaturation did not follow the same pattern as thermal unfolding but rather implied less cooperativity and that the refolding transition increased with increasing protein concentration. Further, NMR experiments indicated that upon refolding the SH3 domain gave rise to more than one conformation. Therefore, our results suggest that the folding of the SH3 domain of II-spectrin does not follow a classical two-state process under high-salt conditions and neutral pH. Heterogeneous folding pathways, which can include folding intermediates as well as misfolded intermediates, might give a more reasonable insight into the folding behaviour of the II-spectrin SH3 domain.

  • 15. Prebil, Sara Drmota
    et al.
    Slapsak, Urska
    Pavsic, Miha
    Ilc, Gregor
    Puz, Vid
    Ribeiro, Euripedes de Almeida
    Anrather, Dorothea
    Hartl, Markus
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Plavec, Janez
    Lenarcic, Brigita
    Djinovic-Carugo, Kristina
    Structure and calcium-binding studies of calmodulin-like domain of human non-muscle alpha-actinin-12016Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikel-id 27383Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The activity of several cytosolic proteins critically depends on the concentration of calcium ions. One important intracellular calcium-sensing protein is alpha-actinin-1, the major actin crosslinking protein in focal adhesions and stress fibers. The actin crosslinking activity of alpha-actinin-1 has been proposed to be negatively regulated by calcium, but the underlying molecular mechanisms are poorly understood. To address this, we determined the first high-resolution NMR structure of its functional calmodulin-like domain (CaMD) in calcium-bound and calcium-free form. These structures reveal that in the absence of calcium, CaMD displays a conformationally flexible ensemble that undergoes a structural change upon calcium binding, leading to limited rotation of the N- and C-terminal lobes around the connecting linker and consequent stabilization of the calcium-loaded structure. Mutagenesis experiments, coupled with mass-spectrometry and isothermal calorimetry data designed to validate the calcium binding stoichiometry and binding site, showed that human non-muscle alpha-actinin-1 binds a single calcium ion within the N-terminal lobe. Finally, based on our structural data and analogy with other alpha-actinins, we provide a structural model of regulation of the actin crosslinking activity of alpha-actinin-1 where calcium induced structural stabilisation causes fastening of the juxtaposed actin binding domain, leading to impaired capacity to crosslink actin.

  • 16.
    Robertsson, Joacim
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Petzold, Katja
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Löfvenberg, Lars
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Folding of Spectrin's SH3 Domain in the Presence of Spectrin Repeats2005Ingår i: Cellular & Molecular Biology Letters, Vol. 10, s. 595-612Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The multifunctional protein spectrin contains several different structural motifs, such as spectrin repeats and a SH3 domain. Both triple-helix spectrin repeats and the SH3 domain are believed to form independent structural entities. In a-spectrins the SH3 domain is localized to repeat 9, where it is positioned between helix B and helix C in the repeat unit. The presence of SH3 in repeat 9 decreases the thermal stability considerably of this repeat unit while another insert in helix C does not seem to affect the stability. Addition of one or two adjacent repeat units increases the thermal stability from ca 25°C to ~41 and ~48°C, respectively. Despite the differences in thermal stability, the folding properties of peptides comprising the SH3 domain only or together with one or more repeats are more or less the same.

  • 17.
    Virel, Ana
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Addario, Barbara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Characterization of Entamoeba histolytica α-actinin22007Ingår i: Molecular and Biochemical Parasitology, Vol. 154, s. 82-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have cloned and characterized a second α-actinin isoform in Entamoeba histolytica. This protein, α-actinin2, has a N-terminal actin-binding domain, a C-terminal calcium-binding domain and an intervening rod domain containing two spectrin repeats. The protein binds and cross-links actin filaments in a calcium-dependent manner. Therefore α-actinin2 is a genuine α-actinin except for the shorter rod domain compared to the rod domain of isoforms of higher organisms.

    A α-actinin-like protein has previous been implicated in the adherence to the host cell and infection. It is therefore possible that α-actinin2 is involved in mechanism of infection, and in particular in reorganisation of the parasite's cytoskeleton that follows on adherence.

    E. histolytica α-actinin2 represents one of the first members of the spectrin superfamily where well defined spectrin repeats are found. The isolation and characterization of this second α-actinin isoform is valuable not only into the study of E. histolytica infection mechanisms, but also for understanding the evolution processes of the spectrin superfamily.

  • 18.
    Virel, Ana
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    A Comparative and Phylogenetic Analysis of the {alpha}-Actinin Rod Domain2007Ingår i: Molecular Biology and Evolution, Vol. 24, nr 10, s. 2254-65Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    -actinin is a ubiquitous actin-binding protein, composed of three domains; an actin-binding domain and a calcium-binding domain at the termini, connected by a rod domain composed by one, two or four spectrin repeats (SR). To understand how the rod domain has evolved during evolution we have analysed and compared the amino acid residue heterogeneity and phylogeny of the spectrin repeats of -actinins of vertebrates, invertebrates, fungus and several protozoa.

    The repeats of vertebrate -actinins show a high degree of similarity whereas repeats of invertebrates, fungi and, in particular, of protozoa are more divergent.

    In the phylogeny, SR1 of all species were clustered together, independent of the number of repeats in the protein. It was also obvious that the second and last repeat in fungi (SR2) grouped with the fourth and last repeat of vertebrates and invertebrates (SR4).

    Therefore the phylogeny implied that the rod domain of the cenancestral -actinin only contained one spectrin repeat. It was also obvious that SR2 of fungi are related to SR4 of vertebrates and invertebrates, implying that in the second intragenic duplication two repeats (i.e. what become SR2 and SR3) were inserted between the initial two repeats that become SR1 and SR4.

  • 19.
    Virel, Ana
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Characterization of entamoeba histolytica alpha-actinin2006Ingår i: Molecular and biochemical parasitology (Print), ISSN 0166-6851, E-ISSN 1872-9428, Vol. 145, nr 1, s. 11-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have cloned, expressed and characterized a alpha-actinin-like protein of Entamoeba histolytica. Analysis of the primary structure reveals that the essential domains of the alpha-actinin protein family are conserved: an N-terminus actin-binding domain, a C-terminus calcium-binding domain and a central helical rod domain. However, the rod domain of this Entamoeba protein is considerably shorter than the rod domain in alpha-actinins of higher organisms. The cloned Entamoeba 63 kDa protein is recognized by conventional alpha-actinin antibodies as well as binds and cross-links filamentous actin and calcium ions in the same manner as alpha-actinins. Despite the shorter rod domain this protein has conserved the most important functions of alpha-actinins. Therefore, it is suggested that this 63 kDa protein is an atypical and ancestral alpha-actinin.

  • 20.
    Virel, Ana
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Backman, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Molecular evolution and structure of α-actinin2004Ingår i: Molecular biology and evolution, ISSN 0737-4038, E-ISSN 1537-1719, Vol. 21, nr 6, s. 1024-1031Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The N-terminal actin-binding domain of -actinin is connected to the C-terminal EF-hands by a rod domain. Because of its ability to form dimers, -actinin can cross-link actin filaments in muscle cells as well as in nonmuscle cells. In the prototypic -actinins, the rod domain contains four triple helical bundles, or so-called spectrin repeats. We have found some atypical -actinins in early diverging organisms, such as protozoa and yeast, where the rod domain contains one and two spectrin repeats, respectively. This implies that the four repeats present in modern -actinins arose after two consecutive intragenic duplications from an -actinin with a single repeat. Further, the evolutionary gene tree of -actinins shows that the appearance of four distinct -actinin isoforms may have occurred after the vertebrate-invertebrate split. The topology of the tree lends support to the hypothesis that two rounds (2R) of genome duplication occurred early in the vertebrate radiation. The phylogeny also considers these atypical isoforms as the most basal to -actinins of vertebrates and other eukaryotes. The analysis also positioned -actinin of the fungi Encephalitozoo cuniculi close to the protozoa, supporting the suggestion that microsporidia are early eukaryotes. Because -actinin is considered the basal member of the spectrin family, our studies will improve the understanding of the origin and evolution of this superfamily.

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