Nebulin alters cross-bridge cycling kinetics and increases thin filament activation. A novel mechanism for increasing tension and reducing tension cost

Murali Chandra, Ranganath Manidi, Steven Ford, Carlos Hidalgo, Christian Witt, Coen Ottenheijm, Siegfried Labeit, Henk Granzier

Research output: Contribution to journalArticlepeer-review

78 Scopus citations

Abstract

Nebulin is a giant filamentous F-actin-binding protein (∼800 kDa) that binds along the thin filament of the skeletal muscle sarcomere. Nebulin is one of the least well understood major muscle proteins. Although nebulin is usually viewed as a structural protein, here we investigated whether nebulin plays a role in muscle contraction by using skinned muscle fiber bundles from a nebulin knock-out (NEB KO) mouse model. We measured force-pCa (-log[Ca2+]) and force-ATPase relations, as well as the rate of tension re-development (ktr) in tibialis cranialis muscle fibers. To rule out any alterations in troponin (Tn) isoform expression and/or status of Tn phosphorylation, we studied fiber bundles that had been reconstituted with bacterially expressed fast skeletal muscle recombinant Tn. We also performed a detailed analysis of myosin heavy chain, myosin light chain, and myosin light chain 2 phosphorylation, which showed no significant differences between wild type and NEB KO. Our mechanical studies revealed that NEB KO fibers had increased tension cost (5.9 versus 4.4 pmol millinewtons -1 mm-1 s-1) and reductions in ktr (4.7 versus 7.3 s-1), calcium sensitivity (pCa50 5.74 versus 5.90), and cooperativity of activation (nH 3.64 versus 4.38). Our findings indicate the following: 1) in skeletal muscle nebulin increases thin filament activation, and 2) through altering cross-bridge cycling kinetics, nebulin increases force and efficiency of contraction. These novel properties of nebulin add a new level of understanding of skeletal muscle function and provide a mechanism for the severe muscle weakness in patients with nebulin-based nemaline myopathy.

Original languageEnglish (US)
Pages (from-to)30889-30896
Number of pages8
JournalJournal of Biological Chemistry
Volume284
Issue number45
DOIs
StatePublished - Nov 6 2009

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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