title: aPKC Inhibition by Par3 CR3 Flanking Regions Controls Substrate Access and Underpins Apical-Junctional Polarization.
abstract: Atypical protein kinase C (aPKC) is a key apical-basal polarity determinant and Par complex component. It is recruited by Par3/Baz (Bazooka in Drosophila) into epithelial apical domains through high-affinity interaction. Paradoxically, aPKC also phosphorylates Par3/Baz, provoking its relocalization to adherens junctions (AJs). We show that Par3 conserved region 3 (CR3) forms a tight inhibitory complex with a primed aPKC kinase domain, blocking substrate access. A CR3 motif flanking its PKC consensus site disrupts the aPKC kinase N lobe, separating P-loop/αB/αC contacts. A second CR3 motif provides a high-affinity anchor. Mutation of either motif switches CR3 to an efficient in vitro substrate by exposing its phospho-acceptor site. In vivo, mutation of either CR3 motif alters Par3/Baz localization from apical to AJs. Our results reveal how Par3/Baz CR3 can antagonize aPKC in stable apical Par complexes and suggests that modulation of CR3 inhibitory arms or opposing aPKC pockets would perturb the interaction, promoting Par3/Baz phosphorylation.
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Erika V
authors.initials: EV
authors.lastname: Soriano
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Marina E
authors.initials: ME
authors.lastname: Ivanova
authors.affiliation: Epithelial Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Georgina
authors.initials: G
authors.lastname: Fletcher
authors.affiliation: Protein Phosphorylation Laboratories, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Philippe
authors.initials: P
authors.lastname: Riou
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Philip P
authors.initials: PP
authors.lastname: Knowles
authors.affiliation: Protein Analysis, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Karin
authors.initials: K
authors.lastname: Barnouin
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Purkiss
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Brenda
authors.initials: B
authors.lastname: Kostelecky
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Saiu
authors.affiliation: Protein Phosphorylation Laboratories, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Linch
authors.affiliation: Epithelial Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Elbediwy
authors.affiliation: Protein Purification Facilities, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Svend
authors.initials: S
authors.lastname: Kjær
authors.affiliation: Peptide Chemistry, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: O'Reilly
authors.affiliation: Protein Analysis, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Ambrosius P
authors.initials: AP
authors.lastname: Snijders
authors.affiliation: Protein Phosphorylation Laboratories, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK; Division of Cancer Studies, King's College London, London SE1 1UL, UK.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Parker
authors.affiliation: Epithelial Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK. Electronic address: barry.thompson@crick.ac.uk.
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Thompson
authors.affiliation: Structural Biology, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK; Institute of Structural and Molecular Biology, School of Biological Science, Birkbeck College, Malet Street, London WC1E 7HX, UK. Electronic address: neil.mcdonald@crick.ac.uk.
authors.forename: Neil Q
authors.initials: NQ
authors.lastname: McDonald
mesh_terms: D022005:Adherens Junctions / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity / Q000502:physiology; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D004848:Epithelium / Q000254:growth & development; D045325:HCT116 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017434:Protein Structure, Tertiary
chemical_list: D029721:Drosophila Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C400774:baz protein, Drosophila; C115015:PKC-3 protein; D011493:Protein Kinase C