Structural basis of the heterodimerization of the MST and RASSF SARAH domains in the Hippo signalling pathway.

Eunha Hwang,Hae-Kap Cheong,Ameeq Ul Mushtaq,Eunhee Kim,Kwon Joo Yeo,Young Ho Jeon,Chaejoon Cheong,Woo Cheol Lee,Hye-Yeon Kim,Kwang Yeon Hwang

doi:10.1107/s139900471400947x

Eunha Hwang, Hae-Kap Cheong + Show 8 more

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https://doi.org/10.1107/s139900471400947x

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Abstract

Despite recent progress in research on the Hippo signalling pathway, the structural information available in this area is extremely limited. Intriguingly, the homodimeric and heterodimeric interactions of mammalian sterile 20-like (MST) kinases through the so-called `SARAH' (SAV/RASSF/HPO) domains play a critical role in cellular homeostasis, dictating the fate of the cell regarding cell proliferation or apoptosis. To understand the mechanism of the heterodimerization of SARAH domains, the three-dimensional structures of an MST1-RASSF5 SARAH heterodimer and an MST2 SARAH homodimer were determined by X-ray crystallography and were analysed together with that previously determined for the MST1 SARAH homodimer. While the structure of the MST2 homodimer resembled that of the MST1 homodimer, the MST1-RASSF5 heterodimer showed distinct structural features. Firstly, the six N-terminal residues (Asp432-Lys437), which correspond to the short N-terminal 3₁₀-helix h1 kinked from the h2 helix in the MST1 homodimer, were disordered. Furthermore, the MST1 SARAH domain in the MST1-RASSF5 complex showed a longer helical structure (Ser438-Lys480) than that in the MST1 homodimer (Val441-Lys480). Moreover, extensive polar and nonpolar contacts in the MST1-RASSF5 SARAH domain were identified which strengthen the interactions in the heterodimer in comparison to the interactions in the homodimer. Denaturation experiments performed using urea also indicated that the MST-RASSF heterodimers are substantially more stable than the MST homodimers. These findings provide structural insights into the role of the MST1-RASSF5 SARAH domain in apoptosis signalling.

Highlights

Recent research into cellular homeostasis has shown that the Hippo signalling pathway, which is mediated by mammalian sterile 20-like kinase (MST, the human orthologue of Hippo), controls organ size in animals and regulates cell proliferation and cell death (Polesello et al, 2006; Ikeda et al, 2009; Del Re et al, 2010; Avruch et al, 2011)
The electron density for the six N-terminal residues of the MST1 SARAH domain (Asp432–Lys437), which correspond to the short N-terminal 310-helix h1 kinked from the h2 helix in the MST1 homodimer investigated in our previous study (Hwang et al, 2007), was missing in the MST1–RASSF5 heterodimer (Fig. 2a and Supplementary Fig. S2b)
The helical structure corresponding to the h2 helix of the MST1 SARAH domain starts from Ser438 in the heterodimer, while that of the MST1 homodimer starts from Val441 (Hwang et al, 2007)

Summary

Introduction

Recent research into cellular homeostasis has shown that the Hippo signalling pathway, which is mediated by mammalian sterile 20-like kinase (MST, the human orthologue of Hippo), controls organ size in animals and regulates cell proliferation and cell death (Polesello et al, 2006; Ikeda et al, 2009; Del Re et al, 2010; Avruch et al, 2011). The key players in this pathway include MST, Ras-association domain family (RASSF) proteins and WW45 (the human orthologue of Salvador), which are tumour suppressors and play significant roles in the immune system and in cardiovascular function (Saucedo & Edgar, 2007; Harvey & Tapon, 2007; Ling et al, 2008). The MST-mediated apoptosis pathway is controlled by its interaction with RASSF family proteins and the WW45. Colocalization of the interaction partners has been observed and has been shown to be dependent on these SARAH domains (Oh et al, 2006; Ling et al, 2008)

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