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PRINCIPAL PUBLICATION AND AUTHORS

Architecture of the MKK6-p38α complex defines the basis of MAPK specificity and activation, P. Juyoux (a), I. Galdadas (b,c), D. Gobbo (b,c), J. von Velsen (a), M. Pelosse (a), M. Tully (d), O. Vadas (e), F.L. Gervasio (b,c,f,g,h), E. Pellegrini (a), M.W. Bowler (a), Science 381, 1217-1225 (2023); https:/doi.org/10.1126/science.add7859 (a) European Molecular Biology Laboratory (EMBL), Grenoble (France) (b) Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, Geneva (Switzerland) (c) School of Pharmaceutical Sciences, University of Geneva, Geneva (Switzerland) (d) ESRF (e) Protein and peptide purification platform, University of Geneva, Geneva (Switzerland) (f) Department of Chemistry, University College London, London (UK) (g) Institute of Structural and Molecular Biology, University College London, London (UK) (h) Swiss Institute of Bioinformatics, Geneva (Switzerland)

REFERENCES

[1] O. Svensson et al., Acta Cryst. D71 1757-1767 (2015).

The simulations show that both the A-loop threonine and tyrosine can access the active site without specific recognition or binding. Extending these simulations to much longer timescales using a Bayesian/maximum- entropy approach and refinement against the SAXS data allowed the reconstruction of the heterogeneous conformational ensemble, aiding understanding of how the two kinases assemble and initiate phosphorylation (Figure 22). The populations of the main states captured in this ensemble, as well as the paths connecting them, show the importance of the N-terminus of MKK6 and the C-lobes of the two kinases in correctly positioning them for phosphorylation. Cellular assays performed with variants of MKK6 N-termini revealed that the length and structure of the N-terminal linker are important in determining specificity between kinase pairs.

Resolving the architecture of MKK6 activating its target MAPK p38α has identified previously unknown interaction sites between the two kinases and made it possible to model the mechanism of activation. The N-termini of MAP2Ks guide the engagement of specific kinases by being tuned to the correct distance for MAP2K/MAPK pairs. Once bound, rather than acting like a classical enzyme and positioning substrates precisely for catalysis, MKK6 creates a zone of proximity, enabling either the tyrosine or threonine to approach the active site, regardless of their state, allowing dual specificity. Through a comprehensive multidisciplinary approach, the study elucidated the architecture and dynamics of the formation of the MKK6-p38α complex. The findings pave the way for targeted drug development and increase understanding of essential kinase signalling cascades.

Fig. 22: Population of states during the assembly of p38α and MKK6 as derived from the fitting of MD derived states to the SAXS curve.