Structure of the regulatory N-domain of human cardiac troponin C in complex with human cardiac troponin I147-163 and bepridil.

Abstract

Cardiac troponin C (cTnC) is the Ca(2+)-dependent switch for contraction in heart muscle and a potential target for drugs in the therapy of heart failure. Ca(2+) binding to the regulatory domain of cTnC (cNTnC) induces little structural change but sets the stage for cTnI binding. A large "closed" to "open" conformational transition occurs in the regulatory domain upon binding cTnI(147-163) or bepridil. This raises the question of whether cTnI(147-163) and bepridil compete for cNTnC.Ca(2+). In this work, we used two-dimensional (1)H,(15)N-heteronuclear single quantum coherence (HSQC) NMR spectroscopy to examine the binding of bepridil to cNTnC.Ca(2+) in the absence and presence of cTnI(147-163) and of cTnI(147-163) to cNTnC.Ca(2+) in the absence and presence of bepridil. The results show that bepridil and cTnI(147-163) bind cNTnC.Ca(2+) simultaneously but with negative cooperativity. The affinity of cTnI(147-163) for cNTnC.Ca(2+) is reduced approximately 3.5-fold by bepridil and vice versa. Using multinuclear and multidimensional NMR spectroscopy, we have determined the structure of the cNTnC.Ca(2+).cTnI(147-163).bepridil ternary complex. The structure reveals a binding site for cTnI(147-163) primarily located on the A/B interhelical interface and a binding site for bepridil in the hydrophobic pocket of cNTnC.Ca(2+). In the structure, the N terminus of the peptide clashes with part of the bepridil molecule, which explains the negative cooperativity between cTnI(147-163) and bepridil for cNTnC.Ca(2+). This structure provides insights into the features that are important for the design of cTnC-specific cardiotonic drugs, which may be used to modulate the Ca(2+) sensitivity of the myofilaments in heart muscle contraction.

• Authors: Xu Wang, Monica X Li, Brian D Sykes
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 277 Issue 34 Pg. 31124-33 (Aug 23 2002) ISSN: 0021-9258 [Print] United States
• PMID: 12060657 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calcium Channel Blockers
• Cardiotonic Agents
• Peptide Fragments
• Troponin C
• Troponin I
• Bepridil
• Calcium

Topics

• Actin Cytoskeleton (drug effects)
• Bepridil (chemistry)
• Calcium (metabolism)
• Calcium Channel Blockers (chemistry)
• Cardiotonic Agents (pharmacology)
• Drug Design
• Humans
• Magnetic Resonance Spectroscopy
• Peptide Fragments (chemistry)
• Troponin C (chemistry)
• Troponin I (chemistry)