Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP).

MTU1 controls intramitochondrial protein synthesis by catalyzing the 2-thiouridine modification of mitochondrial transfer RNAs (mt-tRNAs). Missense mutations in the MTU1 gene are associated with life-threatening reversible infantile hepatic failure. However, the molecular pathogenesis is not well understood. Here, we investigated 17 mutations associated with this disease, and our results showed that most disease-related mutations are partial loss-of-function mutations, with three mutations being particularly severe. Mutant MTU1 is rapidly degraded by mitochondrial caseinolytic peptidase (CLPP) through a direct interaction with its chaperone protein CLPX. Notably, knockdown of CLPP significantly increased mutant MTU1 protein expression and mt-tRNA 2-thiolation, suggesting that accelerated proteolysis of mutant MTU1 plays a role in disease pathogenesis. In addition, molecular dynamics simulations demonstrated that disease-associated mutations may lead to abnormal intermolecular interactions, thereby impairing MTU1 enzyme activity. Finally, clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels, which is partially consistent with the AlphaMissense predictions. These findings provide a comprehensive understanding of MTU1-related diseases, offering prospects for modification-based diagnostics and novel therapeutic strategies centered on targeting CLPP.

Lignans from Euphorbia hirta L.

Five new lignans, euphorhirtins A-D (1-4), 5-methoxyvirgatusin (5), three artefacts, 7S-ethoxyisolintetralin (6), 7R-ethoxyisolintetralin (7), and 7R-ethoxy-3-methoxyisolintetralin (8), together with 13 known ones (9-21) were isolated from the medicinal plant Euphorbia hirta L. The structures of the compounds were elucidated by means of extensive spectroscopic analysis, including 1D and 2D NMR and HR-ESI-MS experiments. The absolute configurations of compound 1 was determined by ECD calculation. The isolates were evaluated for their inhibitory effects against the proliferation of the cancer cell lines (Hep G2, A549, and DU145) and compounds 14 and 18 showed inhibitory activity against the Hep G2 cells with IC50 values 7.2 ± 0.17 and 8.5 ± 0.36 µM.

Dolabellane and Clerodane Diterpenoids from the Twigs and Leaves of Casearia kurzii.

A pair of enantiomeric 15-nordolabellane diterpenoids, (-)- and (+)-caseadolabellols A (1a and 1b), three dolabellane diterpenoids, caseadolabellols B-D (2-4), two dolastane diterpenoids, caseadolastols A and B (5 and 6), 10 clerodane diterpenoids, caseakurzins A-J (7-16), and nine known diterpenoids (17-25) were isolated from the twigs and leaves of Casearia kurzii. The structures of the new compounds were established on the basis of extensive spectroscopic data, and those of compounds 1a, 1b, and 2 were verified by single-crystal X-ray crystallographic analysis. The enantiomers 1a and 1b were separated by chiral-phase HPLC. The absolute configurations were determined by experimental and calculated ECD data, the modified Mosher's method, or literature comparison. Compounds 1a and 5 showed significant quinone reductase-inducing activity in Hepa 1c1c7 cells, while 1b showed moderate activity. Molecular docking studies showed that 1a had greater binding affinity with Nrf2 protein (5FNQ) than 1b. The cytotoxic activity of compounds 1a, 1b, 2-12, 15, and 16 was evaluated, among which compounds 8 and 16 exhibited significant inhibitory activity against the A549 cell line. Compounds 8 and 16 induced the A549 cells to arrest at G2/M and S phases, respectively, and both compounds induced apoptosis in A549 cells.

New terpenoids and triketides from culture of the fungus Botrysphaeria laricina.

Three new isopimarane-type diterpenoids, botrysphins G-I (1-3), a new muurolane-type sesquiterpenoid, 11,12-dihydroxylentideusether (4), and two new triketides, 4-dechlorobotrysphone C (5) and 4,5-dihydroxy-3-methoxy-6-undecanoyloxy-2-cyclohexen-1-one (6), together with one known diterpenoid, sphaeropsidin A (7), one sesquiterpenoid, lentideusether (8), and one triketide sphaeropsidone (9), were isolated from culture of the fungus Botrysphaeria laricina associated with the moss Rhodobryum umgiganteum. The structures of the new compounds were established on the basis of extensive spectroscopic techniques including HRMS and 1D and 2D NMR data. Compounds 1 and 2 exhibited NO inhibitory activity with IC50 values of 13.9 µM and 41.9 µM, respectively. At the same time, these two compounds showed quinone reductase inducing activity with 2.7-fold of induction for 1 at 12.5 µM and 1.6-fold for 2 at 25.0 µM.

Novel secondary metabolites from the endobryophytic fungus Botrysphaeria laricina and their biological activity.

One novel polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) hybrid metabolite, laricinin A (1), two new meroterpenoids, tricycloalternarenes X and Y (2 and 3), one new coumarin, 3,4,7-trihydroxy-6-methylcoumarin (4), together with the known ethyl acetylorsellinate (5), diorcinol K (6), and tricycloalternarenes C and D (7 and 8) were obtained from culture of the fungus Botrysphaeria laricina isolated from the moss Rhodobryum umgiganteum. The structures of the new compounds were elucidated based on extensive spectroscopic techniques including HRMS and 1D and 2D NMR measurements. The absolute configuration of compound 1 was determined by ECD calculation and it was the first example of a novel group of PKS-NRPS hybrids possessing an unprecedented methyldihydropyran-isobutylpyrrolidinone skeleton. Compounds 2, 7, and 8 showed significant quinone reductase inducing activity in Hepa 1c1c7 cells.

Botrysphones A-C and Botrysphins A-F, Triketides and Diterpenoids from the Fungus Botrysphaeria laricina.

Three new triketides, botrysphones A-C (1-3) and six new isopimarane-type diterpenoids, botrysphins A-F (4-9), together with the known triketides sphaeropsidone (10) and chlorosphaeropsidone (11) and diterpenoids sphaeropsidins A and B (12 and 13), were obtained from culture of the fungus Botrysphaeria laricina associated with the moss Rhodobryum umgiganteum. The structures of the new compounds were established on the basis of extensive spectroscopic techniques including HRMS and 1D and 2D NMR data. Compounds 7 and 12 showed significant quinone reductase inducing activity in Hepa 1c1c7 cells.