Capture, mutual inhibition and release mechanism for aPKC-Par6 and its multisite polarity substrate Lgl

Christopher P Earl; Mathias Cobbaut; André Barros-Carvalho; Marina E Ivanova; David C Briggs; Eurico Morais-de-Sá; Peter J Parker; Neil Q McDonald

doi:10.1038/s41594-024-01425-0

Capture, mutual inhibition and release mechanism for aPKC-Par6 and its multisite polarity substrate Lgl

Nat Struct Mol Biol. 2025 Jan 6. doi: 10.1038/s41594-024-01425-0. Online ahead of print.

Authors

Christopher P Earl^#¹, Mathias Cobbaut^#^{2

3}, André Barros-Carvalho^{4

5}, Marina E Ivanova^{1

6}, David C Briggs¹, Eurico Morais-de-Sá^{4

5}, Peter J Parker^{7

8}, Neil Q McDonald^{9

10}

Affiliations

¹ Signalling and Structural Biology Laboratory, Francis Crick Institute, London, UK.
² Signalling and Structural Biology Laboratory, Francis Crick Institute, London, UK. mathias.cobbaut@crick.ac.uk.
³ Protein Phosphorylation Laboratory, Francis Crick Institute, London, UK. mathias.cobbaut@crick.ac.uk.
⁴ Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.
⁵ Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal.
⁶ Imperial College, London, UK.
⁷ Protein Phosphorylation Laboratory, Francis Crick Institute, London, UK.
⁸ School of Cancer and Pharmaceutical Sciences, King's College London, Guy's Campus, London, UK.
⁹ Signalling and Structural Biology Laboratory, Francis Crick Institute, London, UK. neil.mcdonald@crick.ac.uk.
¹⁰ Institute of Structural and Molecular Biology, School of Natural Sciences, Birkbeck College, London, UK. neil.mcdonald@crick.ac.uk.

^# Contributed equally.

PMID: 39762628
DOI: 10.1038/s41594-024-01425-0

Abstract

The mutually antagonistic relationship of atypical protein kinase C (aPKC) and partitioning-defective protein 6 (Par6) with the substrate lethal (2) giant larvae (Lgl) is essential for regulating polarity across many cell types. Although aPKC-Par6 phosphorylates Lgl at three serine sites to exclude it from the apical domain, aPKC-Par6 and Lgl paradoxically form a stable kinase-substrate complex, with conflicting roles proposed for Par6. We report the structure of human aPKCι-Par6α bound to full-length Llgl1, captured through an aPKCι docking site and a Par6^PDZ contact. This complex traps a phospho-S663 Llgl1 intermediate bridging between aPKC and Par6, impeding phosphorylation progression. Thus, aPKCι is effectively inhibited by Llgl1^pS663 while Llgl1 is captured by aPKCι-Par6. Mutational disruption of the Lgl-aPKC interaction impedes complex assembly and Lgl phosphorylation, whereas disrupting the Lgl-Par6^PDZ contact promotes complex dissociation and Lgl phosphorylation. We demonstrate a Par6^PDZ-regulated substrate capture-and-release model requiring binding by active Cdc42 and the apical partner Crumbs to drive complex disassembly. Our results suggest a mechanism for mutual regulation and spatial control of aPKC-Par6 and Lgl activities.