Biology subjects

Onesti, S.

Publications and source records attributed to Onesti, S..

3 recordsLinked to original sources

bioRxiv2026

Charting the Structure and Functional Landscape of the SF3B1 Intrinsically Disordered Region

Despite its essential role in pre-mRNA splicing, the structure and functional significance of the intrinsically disordered N-terminal domain (NTD) of SF3B1, a core component of the SF3b spliceosome complex, remain poorly understood. Here, we combine nuclear magnetic resonance (NMR) spectroscopy, small-angle X-ray scattering (SAXS), biochemistry, bioinformatics approaches, with molecular dynamics simulations to characterize the conformational landscape of the SF3B1-NTD and its phosphorylation-dependent remodelling. Specifically, we focus on the 186-341 region (186-341SF3B1), which contains at least four regulatory phosphorylation sites. We reveal that 186-341SF3B1 is highly dynamic, lacking a stable secondary structure, and that phosphorylation of T211, T235, T313, and T328 induces a shift toward more compact states driven by the formation of intramolecular interactions. Additionally, we unveil that 186-341SF3B1 interacts with RNA primarily via the arginine residues flaking one of the conserved tryptophan-centred motifs present within SF3B1-NTD. These interactions are transient and heterogeneous, reflecting a nonspecific yet sequence-dependent recognition mechanism. Collectively, this study provides a comprehensive description of the conformational landscape and functional features of the SF3B1-NTD, and expands the portfolio of its possible interactors, thus broadening our understanding of how intrinsic disorder, post-translational modifications, and sequence-encoded motifs cooperate to regulate pre-mRNA splicing.

biochemistry↗

bioRxiv2026

Albumin-coated VS1 nanocrystals enable STARD3 inhibition and potentiate fluoropyrimidine therapy in colorectal cancer

Poor aqueous solubility remains a major obstacle to the translational development of targeted anticancer compounds. VS1, a first-in-class inhibitor of the cholesterol-transfer protein STARD3, has emerged as a promising chemosensitizing agent in colorectal cancer (CRC), but its clinical applicability is limited by its poor water solubility. Here, we combine structural biology, nanotechnology, and functional pharmacology to establish STARD3 inhibition as a delivery-enabled strategy to potentiate fluoropyrimidine therapy. To define the molecular basis of STARD3 inhibition, we solved the crystal structure of VS1 bound to the STARD3 ligand-binding domain at 2.1 [A] resolution, revealing direct occupation of the sterol-binding cavity. Molecular dynamics simulations confirmed a stable binding mode and identified the {Omega}1 loop as a dynamic gate regulating ligand binding and dissociation. To overcome the formulation barrier of VS1, we engineered carrier-free, albumin-coated nanocrystals through sonication-assisted nanocrystallization followed by surfactant exchange with human serum albumin. The resulting rod-shaped nanocrystals displayed nanometric size, narrow size distribution, sustained release, and improved aqueous dispersibility, increasing the apparent solubility of VS1 by more than 14-fold while preserving its molecular integrity and crystallinity. Biologically, VS1 selectively potentiated 5-fluorouracil (5-FU) in CRC cells, with synergistic effects restricted to 5-FU-sensitive models and associated with enhanced reactive oxygen species accumulation. Albumin-coated formulation retained the chemosensitizing activity of the free compound. In HCT-116 xenografts, combined treatment with albumin-coated VS1 nanocrystals and 5-FU significantly reduced tumor growth, prolonged tumor doubling time, and increased intratumoral necrosis without exacerbating systemic toxicity. Together, these findings establish that albumin-coated nanocrystals can overcome the delivery limitations of an insoluble STARD3 inhibitor and provide a formulation-enabled strategy to enhance fluoropyrimidine therapy in colorectal cancer. HIGHLIGHTSO_LIA 2.1 [A] crystal structure shows VS1 in the STARD3 sterol-binding cavity C_LIO_LIAlbumin-coated nanocrystals make the insoluble STARD3 inhibitor VS1 deliverable C_LIO_LINanocrystallization raises VS1 apparent solubility >14-fold with sustained release C_LIO_LIVS1 synergizes with 5-FU selectively in 5-FU-sensitive colorectal cancer lines C_LIO_LIAlbumin-nanocrystal VS1 plus 5-FU curbs xenograft growth without added toxicity C_LI

cancer biology↗

bioRxiv2022

FANCJ DNA helicase is recruited to the replisome by AND-1 to ensure genome stability

FANCJ is a DNA helicase linked to Fanconi anemia and frequently mutated in breast and ovarian cancers. If and how FANCJ is recruited to the replisome is unknown. Here, we report that FANCJ directly binds to AND-1 (the vertebrate ortholog of budding yeast Ctf4), a homo-trimeric protein adaptor that connects the CDC45/MCM2-7/GINS replicative DNA helicase with DNA polymerase and several factors at DNA replication forks. We find that the interaction between FANCJ and AND-1 requires the integrity of an evolutionarily conserved Ctf4-interacting protein (CIP) box located between the FANCJ helicase motifs IV and V. Disruption of the FANCJ CIP box significantly reduces FANCJ association with the replisome, causing enhanced DNA damage, decreased replication fork recovery and fork asymmetry in stressful conditions. Cancer-relevant FANCJ CIP box variants display reduced AND-1-binding, a finding that suggests a potential role of the mutated FANCJ alleles in cancer predisposition.

molecular biology↗