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. 2020 Mar 19;8:161. doi: 10.3389/fcell.2020.00161

FIGURE 4.

FIGURE 4

STE20 kinases have distinct domain architectures and regulatory strategies. (A) Schematic of select Drosophila STE20 kinases that have been demonstrated to phosphorylate NDR kinases. The depicted domain organization is based on annotation by UniProtKB/TrEMBL (The UniProt Consortium, 2019); the accession numbers are: Q9VEN3 (GckIII), Q8T0S6 (Hippo), Q9W002 (Misshapen), and A1ZBH7 (Happyhour). Note that Hippo is the sole STE20 kinase with an annotated SARAH (Salvador, Rassf, Hippo) domain. The function of the Citron homology domain (CNH) in NDR kinase regulation is not known. (B) Mutually exclusive SARAH-SARAH binding interactions provide the structural basis for positive and negative regulation of Hippo kinase activity. Formation of Hippo-Rassf antagonizes assembly of Hippo–Hippo or Hippo–Salvador complexes both of which promote full-activation via Hippo trans-autophosphorylation. When in a complex with Salvador, Hippo may be refractive to STRIPAK-mediated inactivation (Bae and Luo, 2018).