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First published online 26 October 2004
doi: 10.1242/jcs.01501

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Differential actin binding along the PEVK domain of skeletal muscle titin

Attila Nagy¹, Paola Cacciafesta^1,*, László Grama¹, András Kengyel¹, András Málnási-Csizmadia² and Miklós S. Z. Kellermayer^1,

¹ Department of Biophysics, University of Pécs, Faculty of Medicine, Szigeti út 12. Pécs 7624, Hungary
² Department of Biochemistry, Eötvös University, Pázmány Péter sétány 1/c., Budapest 1117, Hungary

Author for correspondence (e-mail: miklos.kellermayer.jr{at}aok.pte.hu)

Accepted 18 August 2004

Parts of the PEVK (Pro-Glu-Val-Lys) domain of the skeletal muscle isoform of the giant intrasarcomeric protein titin have been shown to bind F-actin. However, the mechanisms and physiological function of this are poorly understood. To test for actin binding along PEVK, we expressed contiguous N-terminal (PEVKI), middle (PEVKII), and C-terminal (PEVKIII) PEVK segments of the human soleus muscle isoform. We found a differential actin binding along PEVK in solid-state binding, cross-linking and in vitro motility assays. The order of apparent affinity is PEVKII>PEVKI>PEVKIII. To explore which sequence motifs convey the actin-binding property, we cloned and expressed PEVK fragments with different motif structure: PPAK, polyE-rich and pure polyE fragments. The polyE-containing fragments had a stronger apparent actin binding, suggesting that a local preponderance of polyE motifs conveys an enhanced local actin-binding property to PEVK. The actin binding of PEVK may serve as a viscous bumper mechanism that limits the velocity of unloaded muscle shortening towards short sarcomere lengths. Variations in the motif structure of PEVK might be a method of regulating the magnitude of the viscous drag.

Key words: Titin, PEVK, PPAK, polyE, In vitro motility, Elasticity

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