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In meiotic homologous recombination (HR), BRCA2 facilitates loading of the recombinases RAD51 and DMC1 at the sites of double-strand breaks. The HSF2BP-BRME1 complex interacts with BRCA2 to support its function in meiotic HR. In somatic cancer cells ectopically producing HSF2BP, DNA damage can trigger HSF2BP-dependent degradation of BRCA2, which prevents HR. Here we show that, upon binding to BRCA2, HSF2BP assembles into a large ring-shaped 24-mer consisting of three interlocked octameric rings. Addition of BRME1 leads to dissociation of this ring structure, and cancels the disruptive effect of HSF2BP on cancer cell resistance to DNA damage. It also prevents BRCA2 degradation during inter-strand DNA crosslink repair inXenopusegg extracts. We propose that the control of HSF2BP-BRCA2 oligomerization by BRME1 ensures timely assembly of the ring complex that concentrates BRCA2 and controls its turnover, thus promoting meiotic HR.

DNA double strand breaks (DSBs) are deleterious lesions that challenge genome integrity. To mitigate this threat, human cells rely on the activity of multiple DNA repair machineries that are tightly regulated throughout the cell cycle1. In interphase, DSBs are mainly repaired by non-homologous end joining (NHEJ) and homologous recombination (HR)2. However, these pathways are completely inhibited in mitosis3–5, leaving the fate of mitotic DSBs unknown. Here we show that DNA polymerase theta (Polθ)6repairs mitotic DSBs and thereby maintains genome integrity. In contrast to other DSB repair factors, Polθ function is activated in mitosis upon phosphorylation by the Polo-like kinase 1 (PLK1). Phosphorylated Polθ is recruited to mitotic DSBs, where it mediates joining of broken DNA ends, while halting mitotic progression. The lack of Polθ leads to a shortening of mitotic duration and defective repair of mitotic DSBs, resulting in a loss of genome integrity. In addition, we identify mitotic Polθ repair as the underlying cause of the synthetic lethality between Polθ and HR. Our findings reveal the critical importance of mitotic DSB repair for maintaining genome stability.

The combined expression of a handful of pluripotency transcription factors (PluriTFs) in somatic cells can generate induced pluripotent stem cells (iPSCs). Here, we report the structural characterization of disordered regions contained in four important PluriTFs, namely Oct4, Sox2, Nanog and Esrrb. Moreover, many post-translational modifications (PTMs) have been detected on PluriTFs, whose roles are not yet characterized. To help in their study, we also present a method i) to produce well-characterized phosphorylation states of PluriTFs, using NMR analysis, and ii) to use them for pull-downs in stem cell extracts analyzed by quantitative proteomics to identify of Sox2 binders.

Rhoptries and micronemes are essential for host cell invasion and survival of all apicomplexan parasites, which are composed of numerous obligate intracellular protozoan pathogens including Plasmodium falciparum (malaria) and Toxoplasma gondii (toxoplasmosis) that infect humans and animals causing severe diseases. We identified Toxoplasma gondii TgSORT as an essential cargo receptor, which drives the transport of rhoptry (ROP) and microneme (MIC) proteins to ensure the biogenesis of these secretory organelles. The luminal domain of 752 amino acid long situated at the N-terminus end of TgSORT has been described to bind to MIC and ROP proteins. Here, we present an optimized protocol for expression of the entire luminal N-terminus of TgSORT (Tg-NSORT) in the yeast Pichia pastoris. Optimization of its coding sequence, cloning and transformation of the yeast P. pastoris allowed the secretion of Tg-NSORT. The protein was purified and further analyzed by negative staining electron microscopy. In addition, molecular modeling using AlphaFold identified key differences between the human and the T gondii sortilin. The structural features that are only present in T. gondii and other apicomplexan parasites were highlighted. Elucidating the roles of these specific structural features may be useful for designing new therapeutic agents against apicomplexan parasites

Rhoptries and micronemes are essential for host cell invasion and survival of all apicomplexan parasites, which are composed of numerous obligate intracellular protozoan pathogens includingPlasmodium falciparum(malaria) andToxoplasma gondii(toxoplasmosis) that infect humans and animals causing severe diseases. We identifiedToxoplasma gondiiTgSORT as an essential cargo receptor, which drives the transport of rhoptry (ROP) and microneme (MIC) proteins to ensure the biogenesis of these secretory organelles. The luminal ectodomain of 752 amino acid long situated at the N-terminus end of TgSORT has been described to bind to MIC and ROP proteins. Here, we present an optimized protocol for expression of the entire luminal ectodomain of TgSORT (Tg-NSORT) in the yeastPichia pastoris.Optimization of its coding sequence, cloning and transformation of the yeastP. pastorisallowed the secretion of Tg-NSORT. The protein was purified and further analyzed by negative staining electron microscopy. In addition, molecular modeling using AlphaFold identified key differences between human andT gondiisortilin. The structural features that are only present inT. gondiiand other apicomplexan parasites were highlighted. Elucidating the roles of these specific structural features may be useful for designing new therapeutic agents against apicomplexan parasites

Abundant phosphorylation events rule the activity of nuclear proteins involved in gene regulation and DNA repair. These occur mostly on disordered regions of proteins, which often contain multiple phosphosites. Comprehensive and quantitative monitoring of phosphorylation reactions is theoretically achievable at a residue-specific level using 1 H- 15 N NMR spectroscopy, but is often limited by low signal-to-noise at pH\textgreater7 and T\textgreater293K. We developed an improved 13 Cα- 13 CO correlation NMR experiment that works equally at any pH or temperature, i.e. also at those where genuine kinase activities occur. This permits to obtain atomic-resolution information in physiological conditions down to 25 μM. We exemplified the interest of this approach by monitoring phosphorylation reactions, in presence of purified kinases or in cell extracts, on a range of previously problematic targets, namely Mdm2, BRCA2 and Oct4.

BRCA2 plays a prominent role in meiotic homologous recombination (HR). Loss of BRCA2 or several of its meiotic partners causes fertility defects. One of these partners, HSF2BP, was recently discovered as expressed physiologically in germline and ectopically produced in cancer cells. It has an N-terminal coiled coil motif involved in direct binding to the protein BRME1, and both HSF2BP and BRME1 are essential for meiotic HR during spermatogenesis. It also interacts through its C-terminal Armadillo (ARM) domain with a conserved region of BRCA2 of unknown function. We analyzed the structural properties and functional consequences of the BRCA2-HSF2BP interaction and tested the emerging model of its involvement in meiosis. We solved the crystal structure of the complex between the BRCA2 fragment that is disordered in solution and the HSF2BP dimeric ARM domain. This revealed two previously unrecognized BRCA2 repeats that each interact with one ARM monomer from two different dimers. BRCA2 binding triggers ARM tetramerization, resulting in a complex containing two BRCA2 fragments connecting two ARM dimers. The 3D structures of the BRCA2 repeats are superimposable, revealing conserved contacts between the BRCA2 residues defining the repeats and the HSF2BP residues lining the groove of the ARM. This large interface is responsible for the nanomolar affinity of the interaction, significantly stronger than any other measured interaction involving BRCA2. Deleting exon 12 from Brca2, encoding the first repeat, disrupted BRCA2 binding to HSF2BP in vitro and in cells. However, Brca2Δ12/Δ12 mice with the same deletion were fertile and did not show any meiotic defects, contrary to the prediction from the model positing that HSF2BP acts as a meiotic localizer of BRCA2. We conclude that the high-affinity interaction between BRCA2 and HSF2BP and the resulting HSF2BP oligomerization are not required for RAD51 and DMC1 recombinase localization to meiotic double strand breaks and for productive meiotic HR.

In line with their high accessibility, disordered proteins are exquisite targets of kinases. Eukaryotic organisms use the so-called intrinsically disordered proteins (IDPs) or intrinsically disordered regions of proteins (IDRs) as molecular switches carrying intracellular information tuned by reversible phosphorylation schemes. Solvent-exposed serines and threonines are abundant in IDPs, and, consistently, kinases often modify disordered regions of proteins at multiple sites. In this context, nuclear magnetic resonance (NMR) spectroscopy provides quantitative, residue-specific information that permits mapping of phosphosites and monitoring of their individual kinetics. Hence, NMR monitoring emerges as an in vitro approach, complementary to mass-spectrometry or immuno-blotting, to characterize IDP phosphorylation comprehensively. Here, we describe in detail generic protocols for carrying out NMR monitoring of IDP phosphorylation, and we provide a number of practical insights that improve handiness and reproducibility of this method.

Abundant phosphorylation events control the activity of nuclear proteins involved in gene regulation and DNA repair. These occur mostly on disordered regions of proteins, which often contain multiple phosphosites. Comprehensive and quantitative monitoring of phosphorylation reactions is theoretically achievable at a residue-specific level using

International audience; In line with their high accessibility, disordered proteins are exquisite targets of kinases. Eukaryotic organisms use the so-called intrinsically disordered proteins (IDPs) or intrinsically disordered regions of proteins (IDRs) as molecular switches carrying intracellular information tuned by reversible phosphorylation schemes. Solvent-exposed serines and threonines are abundant in IDPs, and, consistently, kinases often modify disordered regions of proteins at multiple sites. In this context, nuclear magnetic resonance (NMR) spectroscopy provides quantitative, residue-specific information that permits mapping of phosphosites and monitoring of their individual kinetics. Hence, NMR monitoring emerges as an in vitro approach, complementary to mass-spectrometry or immuno-blotting, to characterize IDP phosphorylation comprehensively. Here, we describe in detail generic protocols for carrying out NMR monitoring of IDP phosphorylation, and we provide a number of practical insights that improve handiness and reproducibility of this method.