Structure of Crumbs tail in complex with the PALS1 PDZ-SH3-GK tandem reveals a highly specific assembly mechanism for the apical Crumbs complex.
The Crumbs (Crb) complex, formed by Crb, PALS1, and PATJ, is evolutionarily conserved in metazoans and acts as a master cell-growth 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, the mechanistic 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 supramodule with 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.
Division of Life Science, State Key Laboratory of Molecular Neuroscience and.
Youjun
Y
Li
Division of Life Science, State Key Laboratory of Molecular Neuroscience and Center of Systems Biology and Human Health, School of Science and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China; Department of Biology, South University of Science and Technology of China, Shenzhen 518055, China; and.
Zhiyi
Z
Wei
Division of Life Science, State Key Laboratory of Molecular Neuroscience and Center of Systems Biology and Human Health, School of Science and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China;
Yan
Y
Yan
Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912.
Qingwen
Q
Wan
Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912.
Quansheng
Q
Du
Division of Life Science, State Key Laboratory of Molecular Neuroscience and Center of Systems Biology and Human Health, School of Science and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China; mzhang@ust.hk.
Mingjie
M
Zhang
D000595:Amino Acid Sequence; D000818:Animals; D016764:Cell Polarity; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D051528:Guanylate Kinases / Q000737:chemistry; D061985:Madin Darby Canine Kidney Cells; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D054731:PDZ Domains; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D018909:src Homology Domains
D008565:Membrane Proteins; D051528:Guanylate Kinases
MAGUK; PBM; Stardust; cell polarity; supramodule