A 1H NMR study of a ternary peptide complex that mimics the interaction between troponin C and troponin I

Abstract

The troponin I peptide Nα‐acetyl TnI (104–115) amide (TnIp) represents the minimum sequence necessary for inhibition of actomyosin ATPase activity of skeletal muscle (Talbot, J.A. & Hodges, R.S., 1981, J. Biol. Chem. 256, 2798–3802; Van Eyk, J.E. & Hodges, R.S., 1988, J. Biol. Chem. 263, 1726–1732; Van Eyk, J.E., Kay, C.M., & Hodges, R.S., 1991, Biochemistry 30, 9974–9981). In this study, we have used 1H NMR spectroscopy to compare the binding of this inhibitory TnI peptide to a synthetic peptide heterodimer representing site III and site IV of the C‐terminal domain of troponin C (TnC) and to calcium‐saturated skeletal TnC. The residues whose 1H NMR chemical shifts are perturbed upon TnIp binding are the same in both the site III/site IV heterodimer and TnC. These residues include F102, I104, F112, I113, I121, I149, D150, F151, and F154, which are all found in the C‐terminal domain hydrophobic pocket and antiparallel β‐sheet region of the synthetic site III/site IV heterodimer and of TnC. Further, the affinity of TnIp binding to the heterodimer (Kd = 192 + 37 μM) was found to be similar to TnIp binding to TnC (48 + 18 μM [Campbell, A.P., Cachia, P.J., & Sykes, B.D., 1991, Biochem. Cell Biol. 69, 674–681]). The results indicate that binding of the inhibitory region of TnI is primarily to the C‐terminal domain of TnC. The results also indicate how well the synthetic peptide heterodimer mimics the C‐terminal domain of TnC in structure and functional interactions. Copyright © 1992 The Protein Society