Conserved salt-bridge competition triggered by phosphorylation regulates the protein interactome
Edited by Natalia Jura, University of California, San Francisco, CA, and accepted by Editorial Board Member Brenda A. Schulman November 10, 2017 (received for review June 27, 2017)
Significance
Phosphorylation is a ubiquitous modification that has been implicated in signaling and other functions, but the atomic-level mechanisms are not completely understood. We identify a salt-bridge competition or “theft” mechanism wherein a phosphoserine, but not a phosphomimetic, breaks a pre-existing salt bridge, initiating a partial unfolding event and promoting new protein interactions. Structural elements underlying the theft occurred early in evolution and are found in 10% of homo-oligomers and 30% of hetero-oligomers. These findings identify a facile and evolutionarily accessible mechanism for reorganizing salt bridges and other electrostatic networks with only a single mutation to trigger a functional switch.
Abstract
Phosphorylation is a major regulator of protein interactions; however, the mechanisms by which regulation occurs are not well understood. Here we identify a salt-bridge competition or “theft” mechanism that enables a phospho-triggered swap of protein partners by Raf Kinase Inhibitory Protein (RKIP). RKIP transitions from inhibiting Raf-1 to inhibiting G-protein–coupled receptor kinase 2 upon phosphorylation, thereby bridging MAP kinase and G-Protein–Coupled Receptor signaling. NMR and crystallography indicate that a phosphoserine, but not a phosphomimetic, competes for a lysine from a preexisting salt bridge, initiating a partial unfolding event and promoting new protein interactions. Structural elements underlying the theft occurred early in evolution and are found in 10% of homo-oligomers and 30% of hetero-oligomers including Bax, Troponin C, and Early Endosome Antigen 1. In contrast to a direct recognition of phosphorylated residues by binding partners, the salt-bridge theft mechanism represents a facile strategy for promoting or disrupting protein interactions using solvent-accessible residues, and it can provide additional specificity at protein interfaces through local unfolding or conformational change.
Data Availability
Data deposition: The atomic coordinates and structure factors have been deposited in the RCSB Protein Data Bank, www.rcsb.org [PDB ID codes 6ENS (RKIP) and 6ENT (Δ143-146 variant)].
Acknowledgments
We thank Helmholtz-Zentrum Berlin for the allocation of synchrotron radiation beamtime and the staff of beamline MX 14.1 for technical assistance and Drs. Gianluigi Veglia and Jonggul Kim for valuable discussions. This work was supported by Grants GM087630 (to M.R.R.), GM55694 (to T.R.S.), Deutsche Forschungsgemeinschaft FZ82 (to K.L., C.K., and H.S.) and SFB688 and TPA17 (to K.L.), the German Ministry of Research and Education and the Ministry for Innovation, Science and Research of the Federal State of North Rhine-Westphalia (K.L.).
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Information & Authors
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Copyright
© 2017. Published under the PNAS license.
Data Availability
Data deposition: The atomic coordinates and structure factors have been deposited in the RCSB Protein Data Bank, www.rcsb.org [PDB ID codes 6ENS (RKIP) and 6ENT (Δ143-146 variant)].
Submission history
Published online: December 5, 2017
Published in issue: December 19, 2017
Keywords
Acknowledgments
We thank Helmholtz-Zentrum Berlin for the allocation of synchrotron radiation beamtime and the staff of beamline MX 14.1 for technical assistance and Drs. Gianluigi Veglia and Jonggul Kim for valuable discussions. This work was supported by Grants GM087630 (to M.R.R.), GM55694 (to T.R.S.), Deutsche Forschungsgemeinschaft FZ82 (to K.L., C.K., and H.S.) and SFB688 and TPA17 (to K.L.), the German Ministry of Research and Education and the Ministry for Innovation, Science and Research of the Federal State of North Rhine-Westphalia (K.L.).
Notes
This article is a PNAS Direct Submission. N.J. is a guest editor invited by the Editorial Board.
Authors
Competing Interests
The authors declare no conflict of interest.
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