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. 1992 Jul;1(7):945–955. doi: 10.1002/pro.5560010713

Role of interchain alpha-helical hydrophobic interactions in Ca2+ affinity, formation, and stability of a two-site domain in troponin C.

O D Monera 1, G S Shaw 1, B Y Zhu 1, B D Sykes 1, C M Kay 1, R S Hodges 1
PMCID: PMC2142150  PMID: 1304377

Abstract

We have previously shown that a 34-residue synthetic peptide representing the calcium-binding site III of troponin C formed a symmetric two-site dimer consisting of two helix-loop-helix motifs arranged in a head-to-tail fashion (Shaw, G.S., Hodges, R.S., & Sykes, B.D., 1990, Science 249, 280-283). In this study the hydrophobicities of the alpha-helices were altered by replacing L-98 and F-102 in the N-terminal region and/or I-121 and L-122 in the C-terminal region with alanine residues. Our results showed that substitution of hydrophobic residues either in the N- or C-terminal region have little effect on alpha-helix formation but resulted in a 100- and 300-fold decrease in Ca2+ affinity, respectively. Simultaneous substitution of both hydrophobes in the N- and C-terminal region resulted in a 1,000-fold decrease in Ca2+ affinity. Data from guanidine hydrochloride denaturation studies suggested that intermolecular interactions occur and that the less hydrophobic analogs had a lower overall conformational stability. These data support the contention that the hydrophobic residues are important in the formation of the two-site domain in troponin C, and this hydrophobic association stabilizes Ca2+ affinity.

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Selected References

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