Crystal structures of designed armadillo repeat proteins: Implications of construct design and crystallization conditions on overall structure

Authors

  • Christian Reichen,

    1. Department of Biochemistry, University of Zürich, Zürich, Switzerland
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  • Chaithanya Madhurantakam,

    1. Department of Biochemistry, University of Zürich, Zürich, Switzerland
    Current affiliation:
    1. Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium
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  • Andreas Plückthun,

    Corresponding author
    1. Department of Biochemistry, University of Zürich, Zürich, Switzerland
    • Correspondence to: Andreas Plückthun, Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. E-mail: plueckthun@bioc.uzh.ch and Peer R. E. Mittl, Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. E-mail: mittl@bioc.uzh.ch

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  • Peer R. E. Mittl

    Corresponding author
    1. Department of Biochemistry, University of Zürich, Zürich, Switzerland
    • Correspondence to: Andreas Plückthun, Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. E-mail: plueckthun@bioc.uzh.ch and Peer R. E. Mittl, Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. E-mail: mittl@bioc.uzh.ch

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Abstract

Designed armadillo repeat proteins (dArmRP) are promising modular proteins for the engineering of binding molecules that recognize extended polypeptide chains. We determined the structure of a dArmRP containing five internal repeats and 3rd generation capping repeats in three different states by X-ray crystallography: without N-terminal His6-tag and in the presence of calcium (YM5A/Ca2+), without N-terminal His6-tag and in the absence of calcium (YM5A), and with N-terminal His6-tag and in the presence of calcium (His-YM5A/Ca2+). All structures show different quaternary structures and superhelical parameters. His-YM5A/Ca2+ forms a crystallographic dimer, which is bridged by the His6-tag, YM5A/Ca2+ forms a domain-swapped tetramer, and only in the absence of calcium and the His6-tag, YM5A forms a monomer. The changes of superhelical parameters are a consequence of calcium binding, because calcium ions interact with negatively charged residues, which can also participate in the modulation of helix dipole moments between adjacent repeats. These observations are important for further optimizations of dArmRPs and provide a general illustration of how construct design and crystallization conditions can influence the exact structure of the investigated protein.

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