Infrared spectroscopic study of the binding of divalent cations to Akazara scallop troponin C: The effect of the methylene side chain of glutamate residue

✍ Scribed by Masayuki Nara; Fumiaki Yumoto; Hiroyuki Kagi; Masaru Tanokura

• Publisher: Wiley (John Wiley & Sons)
• Year: 2008
• Tongue: English
• Weight: 196 KB
• Volume: 89
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.20962

✦ Synopsis

Abstract

Akazara scallop striated adductor muscle troponin C (TnC) binds only one Ca^2+^ because the three EF‐hand motifs are short of critical residues for the coordination of Ca^2+^. Fourier‐transform infrared spectroscopy was applied to study coordination structures of M^2+^ (= Mg^2+^, Ca^2+^, Sr^2+^, and Ba^2+^) bound in an Akazara scallop TnC mutant (E142D) and the wild‐type TnC C‐lobe in D~2~O solution. The region of the COO^−^ antisymmetric stretch provides information regarding the coordination modes of a COO^−^ group to a metal ion. The side chain COO^−^ group of Asp142 did not bind to Ca^2+^ in the bidentate coordination mode, suggesting that the absence of a methylene group is critical for the Ca^2+^ coordination structure of Akazara scallop TnC (Nara et al., Vib Spect 2006, 42, 188–191). The present study has shown that the absence of a methylene group is not compensated for by a larger metal ion such as Sr^2+^ or Ba^2+^. CD spectra showed that the secondary structures are conserved between M^2+^‐free (apo), Mg^2+^‐loaded, Ca^2+^‐loaded, Sr^2+^‐loaded, and Ba^2+^‐loaded states, which was consistent with the results estimated from their amide I band patterns. The metal‐ligand interaction at position 12 of site IV is discussed in comparison with the coordination mode of the side chain COO^−^ group of the wild‐type TnC C‐lobe. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 595–599, 2008.

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