• Juxtanodin is an intrinsically disordered F-actin-binding protein.

      Ruskamo, Salla; Chukhlieb, Maryna; Vahokoski, Juha; Bhargav, Saligram Prabhakar; Liang, Fengyi; Kursula, Inari; Kursula, Petri (2012)
      Juxtanodin, also called ermin, is an F-actin-binding protein expressed by oligodendrocytes, the myelin-forming cells of the central nervous system. While juxtanodin carries a short conserved F-actin-binding segment at its C terminus, it otherwise shares no similarity with known protein sequences. We carried out a structural characterization of recombinant juxtanodin in solution. Juxtanodin turned out to be intrinsically disordered, as evidenced by conventional and synchrotron radiation CD spectroscopy. Small-angle X-ray scattering indicated that juxtanodin is a monomeric, highly elongated, unfolded molecule. Ensemble optimization analysis of the data suggested also the presence of more compact forms of juxtanodin. The C terminus was a strict requirement for co-sedimentation of juxtanodin with microfilaments, but juxtanodin had only mild effects on actin polymerization. The disordered nature of juxtanodin may predict functions as a protein interaction hub, although F-actin is its only currently known binding partner.
    • Raver1 is an integral component of muscle contractile elements.

      Zieseniss, Anke; Schroeder, Ulrich; Buchmeier, Sabine; Schoenenberger, Cora-Ann; van den Heuvel, Joop; Jockusch, Brigitte M; Illenberger, Susanne; Cell Biology, Zoological Institute, Technical University of Braunschweig, Biocentre, Spielmannstrasse 7, 38092 Braunschweig, Germany. (2007-03)
      Raver1, a ubiquitously expressed protein, was originally identified as a ligand for metavinculin, the muscle-specific isoform of the microfilament-associated protein vinculin. The protein resides primarily in the nucleus, where it colocalises and may interact with polypyrimidine-tract-binding protein, which is involved in alternative splicing processes. During skeletal muscle differentiation, raver1 translocates to the cytoplasm and eventually targets the Z-line of sarcomeres. Here, it colocalises with metavinculin, vinculin and alpha-actinin, all of which have biochemically been identified as raver1 ligands. To obtain more information about the potential role of raver1 in muscle structure and function, we have investigated its distribution and fine localisation in mouse striated and smooth muscle, by using three monoclonal antibodies that recognise epitopes in different regions of the raver1 protein. Our immunofluorescence and immunoelectron-microscopic results indicate that the cytoplasmic accumulation of raver1 is not confined to skeletal muscle but also occurs in heart and smooth muscle. Unlike vinculin and metavinculin, cytoplasmic raver1 is not restricted to costameres but additionally represents an integral part of the sarcomere. In isolated myofibrils and in ultrathin sections of skeletal muscle, raver1 has been found concentrated at the I-Z-I band. A minor fraction of raver1 is present in the nuclei of all three types of muscle. These data indicate that, during muscle differentiation, raver1 might link gene expression with structural functions of the contractile machinery of muscle.