Conserved salt-bridge competition triggered by phosphorylation regulates the protein interactome

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.

Citation
Skinner JJ, Wang S, Lee J, Ong C, Sommese R, et al. (2017) Conserved salt-bridge competition triggered by phosphorylation regulates the protein interactome. Proceedings of the National Academy of Sciences: 201711543. Available: http://dx.doi.org/10.1073/pnas.1711543114.

Acknowledgements
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.).

Publisher
Proceedings of the National Academy of Sciences

Journal
Proceedings of the National Academy of Sciences

DOI
10.1073/pnas.1711543114

Additional Links
http://www.pnas.org/content/early/2017/12/04/1711543114.abstract

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