title: Structural basis for interaction between the conserved cell polarity proteins Inscuteable and Leu-Gly-Asn repeat-enriched protein (LGN).
abstract: Interaction between the mammalian cell polarity proteins mInsc (mammalian homologue of Inscuteable) and Leu-Gly-Asn repeat-enriched protein (LGN), as well as that between their respective Drosophila homologues Inscuteable and Partner of Inscuteable (Pins), plays crucial roles in mitotic spindle orientation, a process contributing to asymmetric cell division. Here, we report a crystal structure of the LGN-binding domain (LBD) of human mInsc complexed with the N-terminal tetratricopeptide repeat (TPR) motifs of human LGN at 2.6-Å resolution. In the complex, mInsc-LBD adopts an elongated structure with three binding modules--an α-helix, an extended region, and a β-sheet connected with a loop--that runs antiparallel to LGN along the concave surface of the superhelix formed by the TPRs. Structural analysis and structure-based mutagenesis define residues that are critical for mInsc-LGN association, and reveal that the activator of G-protein signaling 3 (AGS3)-binding protein Frmpd1 [4.1/ezrin/radixin/moesin (FERM) and PSD-95/Dlg/ZO-1 (PDZ) domain-containing protein 1] and its relative Frmpd4 interact with LGN via a region homologous to a part of mInsc-LBD, whereas nuclear mitotic apparatus protein (NuMA) and the C terminus of LGN recognize the TPR domain in a manner different from that by mInsc. mInsc binds to LGN with the highest affinity (K(D) ≈ 2.4 nM) and effectively replaces the Frmpd proteins, NuMA, and the LGN C terminus, suggesting the priority of mInsc in binding to LGN. We also demonstrate, using mutant proteins, that mInsc-LGN interaction is vital for stabilization of LGN and for intracellular localization of mInsc.
authors.affiliation: Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Yuzawa
authors.forename: Sachiko
authors.initials: S
authors.lastname: Kamakura
authors.forename: Yuko
authors.initials: Y
authors.lastname: Iwakiri
authors.forename: Junya
authors.initials: J
authors.lastname: Hayase
authors.forename: Hideki
authors.initials: H
authors.lastname: Sumimoto
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology*; D002850:Chromatography, Gel; D003460:Crystallization; D005453:Fluorescence; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016296:Mutagenesis; D011487:Protein Conformation; D008941:Spindle Apparatus / Q000502:physiology*; D020349:Surface Plasmon Resonance; D014461:Ultracentrifugation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C532305:Frmpd1 protein, human; C102754:GPSM2 protein, human; C509688:INSC protein, human
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