Biology subjects

Mouilleron, S.

Publications and source records attributed to Mouilleron, S..

5 recordsLinked to original sources

bioRxiv2026

Cellular context restricts a promiscuous m6A reader IDR to a single functional effector interface for mRNA decay

N6-methyladenosine (m6A) is a conserved mRNA modification that regulates transcript stability, yet how m6A readers engage effectors remains unknown. We show that during yeast meiosis, the YTH-domain protein Pho92 promotes the decay of m6A-modified transcripts through an uncharacterised, promiscuous intrinsically disordered region (IDR). In vitro, the Pho92 IDR makes multiple contacts with the Ccr4-NOT deadenylase complex and drives tethered reporter decay in the absence of any single subunit. Yet in meiosis, turnover of endogenous m6A-modified transcripts strictly depends on a single interface: direct binding of the Pho92 IDR to Caf40. A single hydrophobic residue substitution is sufficient to abolish Caf40 binding and halt transcript decay. Human YTHDF proteins can functionally substitute for Pho92, but require multiple hydrophobic patches within the IDR for decay activity. Thus, on endogenous m6A-modified transcripts during meiosis, the promiscuous Pho92 IDR is restricted to a single functional interface, revealing unappreciated specificity in m6A-directed mRNA decay.

molecular biology↗

bioRxiv2024

PDZ-directed substrate recruitment is the primary determinant of specific 4E-BP1dephosphorylation by PP1-Neurabin

Protein Phosphatase 1 (PP1) relies on association with PP1-interacting proteins (PIPs) to generate substrate-specific PIP/PP1 holoenzymes, but the lack of well-defined substrates has hindered elucidation of the mechanisms involved. We previously demonstrated that the Phactr1 PIP confers sequence specificity on the Phactr1/PP1 holoenzyme by remodelling the PP1 hydrophobic substrate groove. Phactr1 defines a group of "RVxF-{Phi}{Phi}-R-W" PIPs that all interact with PP1 in a similar fashion. Here we use a PP1-PIP fusion approach to address sequence specificity and identify substrates of the RVxF-{Phi}{Phi}-R-W family PIPs. We show that the four Phactr proteins confer identical sequence specificities on their holoenzymes. We identify the 4E-BP and p70 S6K translational regulators as substrates for the Neurabin/Spinophilin PIPs, implicated in neuronal plasticity, pointing to a role for their holoenzymes in mTORC1-dependent translational control. Biochemical and structural experiments show that in contrast to the Phactrs, substrate recruitment and catalytic efficiency of the PP1-Neurabin and PP1-Spinophilin fusions is primarily determined by substrate interaction with the PDZ domain adjoining their RVxF-{Phi}{Phi}-R-W motifs, rather than by recognition of the remodelled PP1 hydrophobic groove. Thus, even PIPs that interact with PP1 in a similar manner use different mechanisms to ensure substrate selectivity.

molecular biology↗

bioRxiv2024

PP1 PNUTS binds the restrictor and dephosphorylates RNA pol II CTD Ser5 to stimulate transcription termination

The restrictor, ZC3H4/WDR82, is the major termination factor for antisense transcription from bidirectional promoters, but its mechanism is poorly understood. We report that ZC3H4/WDR82 co-purifies with PP1 phosphatase and PP1 phosphatase nuclear targeting subunit, PNUTS, which binds directly to the WDR82 subunit of restrictor. AlphaFold predicts a quaternary complex, PPWZ, in which PP1-associated PNUTS and ZC3H4 both contact WDR82. To investigate the role of protein dephosphorylation in PPWZ activity, we expressed a substrate trap comprising inactive PP1H66K linked to the PNUTS C-terminus. PP1H66K-PNUTS binds pol II large subunit and nuclear exosome components. PP1H66K-PNUTS, but not PP1WT-PNUTS, functions as a dominant-negative inhibitor of antisense termination and CTD Ser5 dephosphorylation. Both these activities require the PNUTS WDR82 binding domain that interacts with restrictor. We show that CTD Ser5 hyperphosphorylation is associated with higher processivity and reduced pausing that would counteract termination, and propose that Ser5 dephosphorylation by PPWZ is coupled to termination. In summary, we identify the PP1 phosphatase activity of the PPWZ complex as essential for terminator function and propose that this heterotetramer is the physiologically relevant form of restrictor.

molecular biology↗

bioRxiv2024

Structural Insight into the Function of Human Peptidyl Arginine Deiminase 6

Peptidyl arginine deiminase 6 (PADI6) is vital for early embryonic development in mice and humans, yet its function remains elusive. PADI6 is less conserved than other PADIs and it is currently unknown whether it has a catalytic function. Here we have shown that human PADI6 dimerises like hPADIs 2-4, however, does not bind Ca2+ and is inactive in in vitro assays against standard PADI substrates. By determining the crystal structure of hPADI6, we show that hPADI6 is structured in the absence of Ca2+ where hPADI2 and hPADI4 are not, and the Ca-binding sites are not conserved. Moreover, we show that whilst the key catalytic aspartic acid and histidine residues are structurally conserved, the cysteine is displaced far from the active site centre and the hPADI6 active site pocket appears closed through a unique evolved mechanism in hPADI6, not present in the other PADIs. Taken together, these findings provide insight into how the function of hPADI6 may differ from the other PADIs based on its structure and provides a resource for characterising the damaging effect of clinically significant PADI6 variants.

biochemistry↗

bioRxiv2020

Molecular basis for substrate specificity of the Phactr1/PP1 phosphatase holoenzyme

ABSTRACTPPP-family phosphatases such as PP1 have little intrinsic specificity. Cofactors can target PP1 to substrates or subcellular locations, but it remains unclear how they might confer sequence-specificity on PP1. The cytoskeletal regulator Phactr1 is a neuronally-enriched PP1 cofactor that is controlled by G-actin. Structural analysis showed that Phactr1 binding remodels PP1’s hydrophobic groove, creating a new composite surface adjacent to the catalytic site. Using phosphoproteomics, we identified numerous fibroblast and neuronal Phactr1/PP1 substrates, which include cytoskeletal components and regulators. We determined high-resolution structures of Phactr1/PP1 bound to the dephosphorylated forms of its substrates IRSp53 and spectrin αII. Inversion of the phosphate in these holoenzyme-product complexes supports the proposed PPP-family catalytic mechanism. Substrate sequences C-terminal to the dephosphorylation site make intimate contacts with the composite Phactr1/PP1 surface, which are required for efficient dephosphorylation. Sequence specificity explains why Phactr1/PP1 exhibits orders-of-magnitude enhanced reactivity towards its substrates, compared to apo-PP1 or other PP1 holoenzymes.Competing Interest StatementThe authors have declared no competing interest.View Full Text

molecular biology↗