Letter | Published:

Crystallisation of troponin-C

  • An Erratum to this article was published on 26 June 1975

Abstract

TROPONIN is the protein complex that controls the onset of muscular contraction1–3. It has three subunits4: troponin T (Tn-T), troponin I (Tn-I) and troponin C (Tn-C). The complex is bound at regular intervals along the thin filaments, which are composed of a double helix of actin monomers and tropomyosin, which runs along the grooves of the actin helix5–7. Each tropomyosin molecule spans seven actin monomers and one molecule of the troponin complex is bound to each tropomyosin molecule through Tn-T (refs 3 and 6–8). Tn-I binds to actin and Tn-C binds both to Tn-T and Tn-I (refs 3, 4 and 6). In the absence of Ca, Tn-I and Tn-T inhibit contraction by inhibiting the interaction of actin and myosin but in the presence of Ca, Tn-C binds to Ca, the inhibition is reversed and contraction occurs3. We have been interested in crystallising Tn-C in the hope that an eventual crystal structure determination will be helpful in understanding how Ca binding controls the onset of muscle contraction. Here we report the occurrence of a crystalline form of this protein.

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