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Stereospecific binding of a disordered peptide segment mediates BK channel inactivation

An Erratum to this article was published on 15 August 2012

Abstract

A number of functionally important actions of proteins are mediated by short, intrinsically disordered peptide segments1, but the molecular interactions that allow disordered domains to mediate their effects remain a topic of active investigation2,3,4,5. Many K+ channel proteins, after initial channel opening, show a time-dependent reduction in current flux, termed ‘inactivation’, which involves movement of mobile cytosolic peptide segments (approximately 20–30 residues) into a position that physically occludes ion permeation6,7,8. Peptide segments that produce inactivation show little amino-acid identity6,9,10,11,12,13 and tolerate appreciable mutational substitutions13 without disrupting the inactivation process. Solution nuclear magnetic resonance of several isolated inactivation domains reveals substantial conformational heterogeneity with only minimal tendency to ordered structures14,15,16,17. Channel inactivation mechanisms may therefore help us to decipher how intrinsically disordered regions mediate functional effects. Whereas many aspects of inactivation of voltage-dependent K+ channels (Kv) can be described by a simple one-step occlusion mechanism6,7,18,19, inactivation of the voltage-dependent large-conductance Ca2+-gated K+ (BK) channel mediated by peptide segments of auxiliary β-subunits involves two distinguishable kinetic steps20,21. Here we show that two-step inactivation mediated by an intrinsically disordered BK β-subunit peptide involves a stereospecific binding interaction that precedes blockade. In contrast, blocking mediated by a Shaker Kv inactivation peptide is consistent with direct, simple occlusion by a hydrophobic segment without substantial steric requirement. The results indicate that two distinct types of molecular interaction between disordered peptide segments and their binding sites produce qualitatively similar functions.

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Figure 1: Intrinsically disordered β3a N-terminal peptide mimics the two-step inactivation produced by the tethered β3a N terminus.
Figure 2: Intrinsically disordered d- and l- β3a-peptides block BK channels, but only the l- peptide produces unique tail current behaviour.
Figure 3: l- and d- Shaker peptides block Shaker -IR channels in a similar fashion.
Figure 4: BK pore blockers compete with inactivation, but not N terminus binding.

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Acknowledgements

This work was supported by GM-081748 to C.J.L. and the Searle Scholars Program to K.H.-W. We thank E. Morrison and P. Schlesinger for assistance with dynamic light scattering measurements, and C. Frieden and K. Garai for assistance with circular dichroism spectroscopy. We thank H. Jiang, A. Scott and J. Jones for care of oocytes, and J. H. Steinbach and R. Pappu for comments on the manuscript.

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V.G.-P. and X.-H.Z. designed experiments and collected and analysed data. K.H.-W. performed or supervised circular dichroism and NMR determinations. C.J.L. conceived the project, designed research, analysed data and prepared the manuscript.

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Correspondence to Christopher J. Lingle.

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The authors declare no competing financial interests.

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Gonzalez-Perez, V., Zeng, XH., Henzler-Wildman, K. et al. Stereospecific binding of a disordered peptide segment mediates BK channel inactivation. Nature 485, 133–136 (2012). https://doi.org/10.1038/nature10994

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