Artificial binding proteins (Affitins) as probes for conformational changes in secretin PulD |
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Authors: | Krehenbrink Martin Chami Mohamed Guilvout Ingrid Alzari Pedro M Pécorari Frédéric Pugsley Anthony P |
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Affiliation: | 1 Institut Pasteur, Unité de Génétique moléculaire, CNRS URA2172, 25, rue du Dr. Roux, 75724 Paris Cedex 15, France 2 M.E. Müller Institute for Structural Biology, Biozentrum University of Basel, CH 4056 Basel, Switzerland 3 Institut Pasteur, Unité de Biochimie structurale, CNRS URA2185, 25, rue du Dr. Roux, 75724 Paris Cedex 15, France 4 Université de Nantes, CNRS UMR6204, 2 rue de la Houssinière, BP 92208, Nantes 44322 Cedex 3, France |
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Abstract: | The DNA-binding protein Sac7d was previously modified to bind with high affinity to the N domain of the outer membrane secretin PulD from the bacterium Klebsiella oxytoca. Here, we show that binding of the Sac7d derivatives (affitins) to PulD is sensitive to conformational changes caused by denaturant and by the zwitterionic detergent Zwittergent 3-14 routinely used to extract secretins from outer membranes. This sensitivity to the conformational state of PulD allowed us to use the affitins as probes for the native structure of PulD and to devise protocols for examining in vitro synthesized protein in nonionic detergent and for the affinity purification of native PulD using affitins as ligands. When fused to periplasmic PhoA, three affitins inhibited PulD multimerization in vivo and caused loss of function. In two cases, this was likely to be due to dimerization of the affitin by the bound PhoA, as the effect was absent when the affitins were fused to monomeric MalE. In the third case, the MalE and PhoA moieties probably interfered sterically with PulD protomer interactions and, thereby, inhibited multimerization. None of the affitins tested interacted with PulD at sites of protomer interaction or blocked the secretin channel through which exoproteins cross the outer membrane in the Type II secretion pathway of which PulD is a key component. |
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Keywords: | T2SS, Type II protein secretion system EM, electron microscopy NRMSD, normalized root-mean-square deviation POE, polyoxyethylene EDTA, ethylenediaminetetraacetic acid |
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