The highly dynamic oligomeric structure of bradavidin II is unique among avidin proteins

Authors

  • Jenni Leppiniemi,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Amit Meir,

    1. The Alexander Silberman Institute of Life Sciences and The Wolfson Centre for Applied Structural Biology, The Hebrew University of Jerusalem, Jerusalem, Israel
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  • Niklas Kähkönen,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Sampo Kukkurainen,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Juha A. Määttä,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Markus Ojanen,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Janne Jänis,

    1. Department of Chemistry, University of Eastern Finland, Joensuu, Finland
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  • Markku S. Kulomaa,

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
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  • Oded Livnah,

    1. The Alexander Silberman Institute of Life Sciences and The Wolfson Centre for Applied Structural Biology, The Hebrew University of Jerusalem, Jerusalem, Israel
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  • Vesa P. Hytönen

    1. Institute of Biomedical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland
    2. BioMediTech, Tampere, Finland
    3. Fimlab Laboratories, Tampere, Finland
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Correspondence to: Vesa Hytönen, BioMediTech, Biokatu 6, FI-33520 Tampere, Finland. E-mail: vesa.hytonen@uta.fi

Abstract

Bradavidin II is a biotin-binding protein from Bradyrhizobium japonicum that resembles chicken avidin and bacterial streptavidin. A biophysical characterization was carried out using dynamic light scattering, native mass spectrometry, differential scanning calorimetry, and isothermal titration calorimetry combined with structural characterization using X-ray crystallography. These observations revealed that bradavidin II differs from canonical homotetrameric avidin protein family members in its quaternary structure. In contrast with the other avidins, bradavidin II appears to have a dynamic (transient) oligomeric state in solution. It is monomeric at low protein concentrations but forms higher oligomeric assemblies at higher concentrations. The crystal structure of bradavidin II revealed an important role for Phe42 in shielding the bound ligand from surrounding water molecules, thus functionally replacing the L7,8 loop essential for tight ligand binding in avidin and streptavidin. This bradavidin II characterization opens new avenues for oligomerization-independent biotin-binding protein development.

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