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Conformational changes of the chaperone SecB upon binding to a model substrate - bovine pancreatic trypsin inhibitor (BPTI)

Haimann, Michaela M and Akdogan, Yasar and Philipp, Reinhard and Varadarajan, Raghavan and Hinderberger, Dariush and Trommer, Wolfgang E (2011) Conformational changes of the chaperone SecB upon binding to a model substrate - bovine pancreatic trypsin inhibitor (BPTI). In: Biological Chemistry, 392 (10). pp. 849-858.

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Official URL: http://www.reference-global.com/doi/abs/10.1515/BC...

Abstract

SecB is a homotetrameric cytosolic chaperone that forms part of the protein translocation machinery in E. coli. Due to SecB, nascent polypeptides are maintained in an unfolded translocation-competent state devoid of tertiary structure and thus are guided to the translocon. In vitro SecB rapidly binds to a variety of ligands in a non-native state. We have previously investigated the bound state conformation of the model substrate bovine pancreatic trypsin inhibitor (BPTI) as well as the conformation of SecB itself by using proximity relationships based on site-directed spin labeling and pyrene fluorescence methods. It was shown that SecB undergoes a conformational change during the process of substrate binding. Here, we generated SecB mutants containing but a single cysteine per subunit or an exposed highly reactive new cysteine after removal of the nearby intrinsic cysteines. Quantitative spin labeling was achieved with the methanethiosulfonate spin label (MTS) at positions C97 or E90C, respectively. Highfield (W-band) electron paramagnetic resonance (EPR) measurements revealed that with BPTI present the spin labels are exposed to a more polar/hydrophilic environment. Nanoscale distance measurements with double electron-electron resonance (DEER) were in excellent agreement with distances obtained by molecular modeling. Binding of BPTI also led to a slight change in distances between labels at C97 but not at E90C. While the shorter distance in the tetramer increased, the larger diagonal distance decreased. These findings can be explained by a widening of the tetrameric structure upon substrate binding much like the opening of two pairs of scissors.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Walter de Gruyter GmbH & Co. KG.
Keywords: distance measurements;double electron-electron resonance (DEER);electron paramagnetic resonance (EPR);high-field/high-frequency EPR;SecB mutants;spin labeling.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 27 Sep 2011 10:38
Last Modified: 27 Sep 2011 10:38
URI: http://eprints.iisc.ernet.in/id/eprint/40761

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