Abstract
The seven human 14-3-3 isoforms, highly similar yet encoded by distinct genes, are among the top 1% highest-expressed human proteins. 14-3-3 proteins recognize phosphorylated motifs within numerous human or viral proteins. We analyzed by crystallography, fluorescence polarization, mutagenesis and fusicoccin-mediated modulation the structural basis and druggability of 14-3-3 binding to four E6 oncoproteins of tumorigenic HPV. The seven isoforms bound variant and mutated phospho-motifs of E6 and unrelated protein RSK1 with different affinities, albeit following an ordered ranking profile with conserved relative KD ratios. Remarkably, 14-3-3 isoforms obey the same hierarchy when binding to most of their established targets, nicely supported by a recent proteome-wide human complexome map. This knowledge allows predicting the proportions of 14-3-3 isoforms engaged with phosphoproteins in various tissues. Notwithstanding their individual functions, cellular concentrations of 14-3-3 may be collectively adjusted to buffer the strongest phosphorylation outbursts, explaining their expression variations in different tissues and tumors.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Email addresses of the authors: goglg{at}igbmc.fr, kri94_08{at}mail.ru, eberling{at}igbmc.fr, kostmanc{at}igbmc.fr
The manuscript was re-considered and re-written from a wider perspective of the interactome of human 14-3-3 isoforms. More detailed analysis of experimental data within the previous study on the 14-3-3/HPV E6 interaction and comparison with the available literature data and the proteomics data extracted from databases PAXdb and Bioplex 3.0 have allowed to reveal general, hierarchized phosphopeptide-affinity trend displayed by the seven human 14-3-3 isoforms. This trend is found in most of the reported cases on the 14-3-3 interaction with various partner phosphopeptides, regardless of the peptide sequences. Moreover, we show that this trend is perfectly correlated with the sequence identity levels of all seven isoforms with respect to 14-3-3 gamma (typically, the strongest binder), forming also a very well conserved trend. This knowledge was further used to develop a rough predictor tool to estimate the involvement of a given phosphoprotein in complexes with various 14-3-3 isoforms, in a particular cellular contex. This quantitative analysis benefits from the reliable protein abundance data on human 14-3-3 proteins found, for example, in PAXdb database.