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© The Rockefeller University Press, 0021-9525/2001//413 $5.00
The Journal of Cell Biology, Volume 153, Number 2, , 2001 413-428

Myopalladin, a Novel 145-Kilodalton Sarcomeric Protein with Multiple Roles in Z-Disc and I-Band Protein Assemblies

^a European Molecular Biology Laboratory, Heidelberg 69117, Germany
^b Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8654, Japan
^c Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164
^d Department of Anaesthesiology and Intensive Surgical Medicine, University of Mannheim, Mannheim 68167, Germany
^e Department of Cell Biology and Anatomy, University of Arizona, Tucson, Arizona 85721
^f Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85721
Klinikum Mannheim, Theodor-Kutzer-Ufer-1, Mannheim 68167, Germany.(49) 621-383-1971(49) 621-383-2422

labeit{at}embl-heidelberg.de

We describe here a novel sarcomeric 145-kD protein, myopalladin, which tethers together the COOH-terminal Src homology 3 domains of nebulin and nebulette with the EF hand motifs of -actinin in vertebrate Z-lines. Myopalladin's nebulin/nebulette and -actinin–binding sites are contained in two distinct regions within its COOH-terminal 90-kD domain. Both sites are highly homologous with those found in palladin, a protein described recently required for actin cytoskeletal assembly (Parast, M.M., and C.A. Otey. 2000. J. Cell Biol. 150:643–656). This suggests that palladin and myopalladin may have conserved roles in stress fiber and Z-line assembly. The NH₂-terminal region of myopalladin specifically binds to the cardiac ankyrin repeat protein (CARP), a nuclear protein involved in control of muscle gene expression. Immunofluorescence and immunoelectron microscopy studies revealed that myopalladin also colocalized with CARP in the central I-band of striated muscle sarcomeres. Overexpression of myopalladin's NH₂-terminal CARP-binding region in live cardiac myocytes resulted in severe disruption of all sarcomeric components studied, suggesting that the myopalladin–CARP complex in the central I-band may have an important regulatory role in maintaining sarcomeric integrity. Our data also suggest that myopalladin may link regulatory mechanisms involved in Z-line structure (via -actinin and nebulin/nebulette) to those involved in muscle gene expression (via CARP).

Key Words: -actinin • nebulin • palladin • myopalladin • CARP

© 2001 The Rockefeller University Press

Abbreviations used in this paper: CARP, cardiac ankyrin repeat protein; GFP, green fluorescent protein; GST, glutathione S-transferase; SH, Src homology.

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