Probing the pH-dependent structural features of α-KTx12.1, a potassium channel blocker from the scorpion Tityus serrulatus

Authors

  • Sérgio Oyama Jr.,

    1. Center for Brazilian Molecular Structural Biology (CeBiME)—Brazilian Synchrotron Light Laboratory (LNLS), 13084-971 Campinas/SP, Brazil
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    • These authors contributed equally to this work.

  • Primož Pristovšek,

    1. National Institute of Chemistry, 1001 Ljubljana, Slovenia
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    • These authors contributed equally to this work.

  • Lorella Franzoni,

    1. Department of Experimental Medicine, Section of Chemistry and Structural Biochemistry, University of Parma, 43100 Parma, Italy
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    • These authors contributed equally to this work.

  • Thelma A. Pertinhez,

    1. Center for Brazilian Molecular Structural Biology (CeBiME)—Brazilian Synchrotron Light Laboratory (LNLS), 13084-971 Campinas/SP, Brazil
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  • Eugenia Schininá,

    1. Department of Biochemical Sciences, University of Roma, 00133 Roma, Italy
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  • Christian Lücke,

    1. Institute of Biophysical Chemistry, J.W. Goethe University of Frankfurt, 60439 Frankfurt, Germany
    Current affiliation:
    1. Max Planck Research Unit for Enzymology of Protein Folding, 06120 Halle, Germany.
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  • Heinz Rüterjans,

    1. Institute of Biophysical Chemistry, J.W. Goethe University of Frankfurt, 60439 Frankfurt, Germany
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  • Eliane Candiani Arantes,

    1. Department of Physics and Chemistry, University of São Paulo, 14040-903 Ribeirão Preto, Brazil
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  • Alberto Spisni

    Corresponding author
    1. Center for Brazilian Molecular Structural Biology (CeBiME)—Brazilian Synchrotron Light Laboratory (LNLS), 13084-971 Campinas/SP, Brazil
    2. Department of Experimental Medicine, Section of Chemistry and Structural Biochemistry, University of Parma, 43100 Parma, Italy
    • Department of Experimental Medicine, Section of Chemistry and Structural Biochemistry, University of Parma, Via Volturno, 39, 43100 Parma, Italy; fax: +39-0521-903802.
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Abstract

Potassium channels are widespread in living cells and are involved in many diseases. The scorpion toxin α-KTx12.1 interacts with various K+ channels, suggesting its capacity to match diverse channel pores. It is recognized that tissue injuries may affect the pH at toxins site of action, thereby modulating both protein conformation and activity. To better understand its molecular mechanism of action, we studied α-KTx12.1 using pH as a tool to explore its plasticity and NMR in combination with MD calculations to detect it. The toxin solution structure consists of an α-helix and a triple-stranded β-sheet stabilized by four disulfide bridges. The NMR results show, in addition, that His28 possesses an unusually low pKa of 5.2. The best set of protein conformers is obtained at pH 4.5, while at pH 7.0, the reduced number of NOEs resulting from a faster hydrogen exchange does not allow to reach a good structural convergence. Nonetheless, MD calculations show that the toxin structure does not vary significantly in that pH range, while conformational changes and modifications of the surface charge distribution occur when His28 is fully protonated. Moreover, essential dynamics analysis reveals variations in the toxin's coherent motions. In conclusion, His28, with its low pKa value, provides α-KTx12.1 with the ability to preserve its active conformation over a wide pH interval, thus expanding the range of cellular conditions where the toxin can fully exhibit its activity. Overall, the results further underline the role of histidine as a natural controller of proteins' functionality.

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