Effects of ionization on chemical shifts of the surrounding protons of bromelain inhibitor VI

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  • HATANO Ken-ichi
    Department of Biological Sciences, Faculty of Engineering, Gunma University
  • KOJIMA Masaki
    School of Life Science, Tokyo University of Pharmacy and Life Science
  • TANOKURA Masaru
    Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo

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  • Effects of ionization on chemical shifts of the surrounding protons of bromelain inhibitor 4

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Abstract

Proton nuclear magnetic resonance (NMR) titration shifts are a very sensitive indication of proton dissociation from carboxyl groups and of hydrogen-bond formation between carboxylate groups and backbone amide protons. As a model protein, we selected bromelain inhibitor VI (BI-VI), which is a unique double-chain molecule (M r = 5888), and characterized almost all the proton resonances in the pH range of 1.5-9.9 by two-dimensional NMR. In this study, we first examined the ionization effects of Asp13H(β-CO2H) and Glu24H(γ-CO 2H) (superscript letters H and L indicate heavy and light chains, respectively). It was found that their ionization affected the chemical shifts of the surrounding protons through a maximum of seven consecutive covalent bonds, but scarcely through non-covalent bonds. Furthermore, it was revealed that the formation of two hydrogen bonds of Ser4L(NH)-Asp9H(β-CO 2H) and Lys19H(NH)-Asp32H(β-CO2H) influenced not only the chemical shifts of the amide protons of Ser4L and Lys19H but also those of the alpha protons of Asp9H and Asp32H.<br> <br> <br> (Communicated by Masanori OTSUKA, M.J.A.)<br>

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