Abstract
This chapter outlines the structural information obtained from crystallographic studies of Troponin C (TnC) from turkey skeletal muscle. TnC is one of three proteins that make up troponin, a complex that plays a regulatory role in muscle contraction. TnC is a dumb-belled shaped 75Å long molecule, made up of two domains. Each domain is made of two Ca 2+ -binding motifs of helix-loop-helix and the two motifs in a pair are internally related by an approximate noncrystallographic 2-fold rotation. The inter domain helix is an unusual aspect of the TnC molecule, not found so far in any other protein except calmodulin. TnC crystal structure provides the only example of Ca 2+ binding loops in both Ca 2+ -bound and Ca 2+ -free states. The inter-domain helix is a unique feature of TnC and calmodulin. The viability of the transition from the observed Ca 2+ free state to the modeled Ca 2+ bound state was confirmed by carrying out a guided energy minimization. There is at least one pathway through which the opening of the inter-helix angles and the rearrangement of the Ca 2+ binding loops can be accomplished smoothly.
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