Assembly and Molecular Architecture of the Phosphoinositide 3-Kinase p85α Homodimer.

Abstract
Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that are activated by growth factor and G-protein-coupled receptors and propagate intracellular signals for growth, survival, proliferation, and metabolism. p85α, a modular protein consisting of five domains, binds and inhibits the enzymatic activity of class IA PI3K catalytic subunits. Here, we describe the structural states of the p85α dimer, based on data from in vivo and in vitro solution characterization. Our in vitro assembly and structural analyses have been enabled by the creation of cysteine-free p85α that is functionally equivalent to native p85α. Analytical ultracentrifugation studies showed that p85α undergoes rapidly reversible monomer-dimer assembly that is highly exothermic in nature. In addition to the documented SH3-PR1 dimerization interaction, we identified a second intermolecular interaction mediated by cSH2 domains at the C-terminal end of the polypeptide. We have demonstrated in vivo concentration-dependent dimerization of p85α using fluorescence fluctuation spectroscopy. Finally, we have defined solution conditions under which the protein is predominantly monomeric or dimeric, providing the basis for small angle x-ray scattering and chemical cross-linking structural analysis of the discrete dimer. These experimental data have been used for the integrative structure determination of the p85α dimer. Our study provides new insight into the structure and assembly of the p85α homodimer and suggests that this protein is a highly dynamic molecule whose conformational flexibility allows it to transiently associate with multiple binding proteins.

Citation
LoPiccolo, J., Kim, S. J., Shi, Y., Wu, B., Wu, H., Chait, B. T., … Backer, J. M. (2015). Assembly and Molecular Architecture of the Phosphoinositide 3-Kinase p85α Homodimer. Journal of Biological Chemistry, 290(51), 30390–30405. doi:10.1074/jbc.m115.689604

Acknowledgements
We thank Drs. David Cowburn, Gary Gerfen, and Mark Girvin (Albert Einstein Medical School) for helpful discussions. We thank Drs. Gordon Mills (MD Anderson Cancer Center) and Stefan Arold (King Abdullah University of Science and Technology) for sharing unpublished data. We also thank Tsutomu Matsui and Thomas M. Weiss at SSRL (SLAC National Accelerator Laboratory) for assistance with collecting SAXS data and Dina Schneidman-Duhovny (University of California, San Francisco) for discussions on SAXS analysis.

Publisher
Elsevier BV

Journal
Journal of Biological Chemistry

DOI
10.1074/jbc.m115.689604

PubMed ID
26475863

PubMed Central ID
PMC4683262

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S0021925820393340

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