Hexasome-INO80 complex reveals structural basis of noncanonical nucleosome remodeling

Loss of H2A-H2B histone dimers is a hallmark of actively transcribed genes, but how the cellular machinery functions in the context of noncanonical nucleosomal particles remains largely elusive. In this work, we report the structural mechanism for adenosine 5'-triphosphate-dependent chromatin remodeling of hexasomes by the INO80 complex. We show how INO80 recognizes noncanonical DNA and histone features of hexasomes that emerge from the loss of H2A-H2B. A large structural rearrangement switches the catalytic core of INO80 into a distinct, spin-rotated mode of remodeling while its nuclear actin module remains tethered to long stretches of unwrapped linker DNA. Direct sensing of an exposed H3-H4 histone interface activates INO80, independently of the H2A-H2B acidic patch. Our findings reveal how the loss of H2A-H2B grants remodelers access to a different, yet unexplored layer of energy-driven chromatin regulation.

Structural basis for 5'-ETS recognition by Utp4 at the early stages of ribosome biogenesis

Eukaryotic ribosome biogenesis begins with the co-transcriptional assembly of the 90S pre-ribosome. The ‘U three protein’ (UTP) complexes and snoRNP particles arrange around the nascent pre-ribosomal RNA chaperoning its folding and further maturation. The earliest event in this hierarchical process is the binding of the UTP-A complex to the 5'-end of the pre-ribosomal RNA (5'-ETS). This oligomeric complex predominantly consists of β-propeller and α-solenoidal proteins. Here we present the structure of the Utp4 subunit from the thermophilic fungus Chaetomium thermophilum at 2.15 Å resolution and analyze its function by UV RNA-crosslinking (CRAC) and in context of a recent cryo-EM structure of the 90S pre-ribosome. Utp4 consists of two orthogonal and highly basic β-propellers that perfectly fit the EM-data. The Utp4 structure highlights an unusual Velcro-closure of its C-terminal β-propeller as relevant for protein integrity and potentially Utp8 recognition in the context of the pre-ribosome. We provide a first model of the 5'-ETS RNA from the internally hidden 5'-end up to the region that hybridizes to the 3'-hinge sequence of U3 snoRNA and validate a specific Utp4/5'-ETS interaction by CRAC analysis.

Fatal Chaetomium cerebritis in a bone marrow transplant patient

The number of opportunistic infections in the central nervous system (CNS) has been steadily increasing because of a rising number of immunocompromised patients. A rare form of CNS infection can be caused by Chaetomium species, one of the largest genera of saprophytic ascomycetes. The CNS lesions in the present case were caused by Chaetomium atrobrunneum. The main characteristic of almost all Chaetomium species is presence of hairs or setae covering the ascomata. Microbiological studies are the only definitive way to correctly identify this fungal organism. The rapid evolvement of the cerebral infection suggests that the brain tissue provides a favorable environment for growth and proliferation of these fungi. This is the second documented case of a fatal brain abscess caused by Chaetomium atrobrunneum, and the first case report in a bone marrow transplant patient.

Ultrastructural alterations produced by sertaconazole on several opportunistic pathogenic fungi

Sertaconazole is a new synthetic antifungal which has shown promising activity against numerous fungi. The morphological changes induced by the drug at two concentrations, the MIC and 10 times the MIC, during 24 and 48 h on the filamentous opportunistic fungi Aspergillus fumigatus, Chaetomium atrobrunneum and Scedosporium prolificans indicated that the intensity of the ultrastructural breakdown depended on the dose and not on the time of exposure. Common severe alterations of many fungal cells, which could be considered beyond repair, were seen at the cell wall, plasmalemma and cytoplasm levels. The results obtained underline the drug efficacy for those fungi and suggest its applicability as therapeutic agent in the human infections produced by them.