Most AAA+ remodeling motors denature proteins by pulling on the peptide termini of folded substrates, but it is not well-understood how motors produce grip when resisting a folded domain. Here, at single amino-acid resolution, we identify the determinants of grip by measuring how substrate tail sequences alter the unfolding activity of the unfoldase-protease ClpXP. The seven amino acids abutting a stable substrate domain are key, with residues 2-6 forming a core that contributes most significantly to grip. ClpX grips large hydrophobic and aromatic side chains strongly and small, polar, or charged side chains weakly. Multiple side chains interact with pore loops synergistically to strengthen grip. In combination with recent structures, our results support a mechanism in which unfolding grip is primarily mediated by non-specific van der Waal's interactions between core side chains of the substrate tail and a subset of YVG loops at the top of the ClpX axial pore.
- Robert T Sauer
- Tristan A Bell
- Tania A Baker
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Axel T Brunger, Stanford University, United States
© 2019, Bell et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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