The Crumbs (Crb) complex, formed by Crb, PALS1, and PATJ, is evolutionarily conserved in metazoans and acts as a master cellgrowth and -polarity regulator at the apical membranes in polarized epithelia. Crb intracellular functions, including its direct binding to PALS1, are mediated by Crb's highly conserved 37-residue cytoplasmic tail. However, themechanistic basis governing the highly specific Crb-PALS1 complex formation is unclear, as reported interaction between the Crb tail (Crb-CT) and PALS1 PSD-95/DLG/ZO-1 (PDZ) domain is weak and promiscuous. Here we have discovered that the PDZ-Src homolgy 3 (SH3)-Guanylate kinase (GK) tandem of PALS1 binds to Crb-CT with a dissociation constant of 70 nM, which is ∼100-fold stronger than the PALS1 PDZ-Crb-CT interaction. The crystal structure of the PALS1 PDZ-SH3-GK-Crb-CT complex reveals that PDZ-SH3-GK forms a structural supramodulewith all three domains contributing to the tight binding to Crb. Mutations disrupting the tertiary interactions of the PDZ-SH3-GK supramodule weaken the PALS1-Crb interaction and compromise PALS1-mediated polarity establishment in Madin- Darby canine kidney (MDCK) cysts. We further show that specific target binding of other members of membrane-associated guanylate kinases (MAGUKs) (e.g., CASK binding to neurexin) also requires the presence of their PDZ-SH3-GK tandems.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - Dec 9 2014|
- Cell polarity
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