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bioRxiv · 10.1101/2024.09.26.615224

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

Earl, C. P.·Cobbaut, M.·Carvalho, A. B.·Ivanova, M. E.·Briggs, D. C.·Morais-de-Sa, E.·Parker, P. J.·McDonald, N. Q.
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Abstract

The mutually antagonistic kinase-substrate relationship between the apical aPKC-Par6 heterodimer and the basolateral substrate Lgl is key to the establishment and maintenance of cell polarity across metazoa. Although aPKC-Par6 can phosphorylate Lgl at three serine sites to exclude it from the apical domain, paradoxically, aPKC-Par6 and Lgl can also form a stable kinase-substrate complex whose function remains unclear and with conflicting roles proposed for Par6. We report the structure of human aPKC{iota}-Par6 bound to full-length Llgl1, captured through an aPKC{iota} docking site and a Par6PDZ contact. This soluble tripartite complex traps a phospho-S663 Llgl1 intermediate bridging between aPKC and Par6, impeding phosphorylation progression. Thus, aPKC{iota} is effectively inhibited by Llgl1pS663 whilst Llgl1 is captured by aPKC{iota}-Par6. Mutational disruption of Lgl-aPKC interaction impedes complex assembly and Lgl phosphorylation, whereas disrupting the Lgl-Par6PDZ contact promotes complex dissociation and completion of Lgl phosphorylation cycle. We incorporate these findings into a Par6PDZ-regulated substrate capture-and-release model that we demonstrate requires binding by Cdc42-GTP and the apical partner Crumbs to drive complex disassembly. Our results provide an explanation for the opposing roles of Par6 underpinning the spatial control of aPKC-Par6 activity by Lgl relevant to polarised membrane contexts across multi-cellular organisms.

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Earl, C. P., Cobbaut, M., Carvalho, A. B., Ivanova, M. E., Briggs, D. C., Morais-de-Sa, E., Parker, P. J., McDonald, N. Q.. 2024-09-26. Capture, mutual inhibition and release mechanism for aPKC-Par6 and its multi-site polarity substrate Lgl. https://doi.org/10.1101/2024.09.26.615224

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