Biomedical subjects

Mario J Borgnia

Publications and source records attributed to Mario J Borgnia.

4 recordsLinked to original sources

PubMed2026

Cryo-EM structures of Candida albicans chitin synthase Chs1 reveal a druggable translocation channel.

Invasive candidiasis is a leading cause of hospital-acquired bloodstream infections with high mortality. While the fungal cell wall is an excellent therapeutic target, inhibitor development against the essential chitin synthase (Chs) has been hampered by the absence of structural and mechanistic understanding of class II Chs, which contribute to fungal viability. Here we present cryo-electron microscopy structures of Candida albicans class II Chs (CaChs1) at 2.93-3.38 Å resolution, providing insights into its mechanisms of early elongation, chito-oligomer translocation and inhibition by the CaChs1-specific non-competitive inhibitor diynyl arylamine (DA). Chitin elongation and translocation are coupled to coordinated motion of the glycosyltransferase domain and the dimer interface. Notably, DA binds within the chitin translocation channel where a regulatory lipid resides and inhibits the enzyme by occluding product polymer extrusion. Importantly, DA showed potent synergy with the class I Chs inhibitor nikkomycin Z against C. albicans and Candida auris. These findings establish the chitin translocation channel as a druggable site for rational antifungal design.

Journal Article↗

PubMed2026

Structural insights into RNA phosphorylation by the RNase PNK module of the human rixosome complex.

The mammalian rixosome complex is a large multi-subunit complex that plays essential roles in ribosome assembly and heterochromatin maintenance. Three structural proteins form the stable core of the rixosome to which three enzymatic modules are flexibly tethered including an RNA processing module, AAA-ATPase, and SUMO protease. The RNA processing module is formed by RNase PNK, a tetrameric assembly comprising two copies each of the LAS1L endoribonuclease (RNase) and the NOL9 polynucleotide kinase (PNK). Using single particle cryo-EM, we determined ATPγS and AMP-PNP/RNA-bound structures of human RNase PNK. The structures revealed the overall butterfly-like architecture of the complex and provide new insights into the mechanism of RNA accommodation and 5' hydroxyl phosphorylation within the NOL9 active site. Through reconstitution studies and molecular modeling, we establish how RNase PNK is incorporated into the larger rixosome complex by a distinct domain of LAS1L. Finally, we show that the human 5'-3' exoribonuclease XRN2 directly associates with RNase PNK and selectively degrades NOL9-phosphorylated RNA in vitro, thereby linking ITS2 processing by the rixosome to processive exonucleolytic decay. Collectively this work establishes an updated model for how the rixosome integrates its diverse enzymatic activities to regulate ITS2 processing.

Humans↗

PubMed2025

Structural Basis of Cold and Menthol Sensing by TRPM8.

The transient receptor potential melastatin member 8 (TRPM8) is a polymodal ion channel that senses cold and menthol in mammals. Despite prior structural studies, the mechanisms by which cold and menthol activate TRPM8 remain unresolved. Here, we present cryo-EM structures representing the cold and menthol-dependent activation trajectories, combined with extensive functional analyses. We captured snapshots of cooling-dependent pore opening, which involves dramatic pore rearrangement, suggesting a mechanism for cold sensing. Moreover, menthol binds dynamically to induce channel activation, which may underlie menthol specificity for TRPM8. Finally, we show how TRPM8 integrates multiple modalities (cold and menthol) through overlapping but non-identical pathways, revealing the temperature-specific "cold spot". These findings enhance our understanding of the molecular basis of physically and chemically induced cool sensation in mammals.

Journal Article↗

PubMed2023

Structural basis for pre-tRNA recognition and processing by the human tRNA splicing endonuclease complex.

Throughout bacteria, archaea and eukarya, certain tRNA transcripts contain introns. Pre-tRNAs with introns require splicing to form the mature anticodon stem loop. In eukaryotes, tRNA splicing is initiated by the heterotetrameric tRNA splicing endonuclease (TSEN) complex. All TSEN subunits are essential, and mutations within the complex are associated with a family of neurodevelopmental disorders known as pontocerebellar hypoplasia (PCH). Here, we report cryo-electron microscopy structures of the human TSEN-pre-tRNA complex. These structures reveal the overall architecture of the complex and the extensive tRNA binding interfaces. The structures share homology with archaeal TSENs but contain additional features important for pre-tRNA recognition. The TSEN54 subunit functions as a pivotal scaffold for the pre-tRNA and the two endonuclease subunits. Finally, the TSEN structures enable visualization of the molecular environments of PCH-causing missense mutations, providing insight into the mechanism of pre-tRNA splicing and PCH.

Humans↗