Biology subjects

Stirpe, A.

Publications and source records attributed to Stirpe, A..

3 recordsLinked to original sources

bioRxiv2026

The HMD domain of the PAF complex primes Rad6-Bre1 E3 ligase complexes for H2B ubiquitination

Mono-ubiquitination of histone H2B (H2Bub) is deposited by Bre1-type E3 ubiquitin ligase complexes during transcription elongation and is critical for chromatin organization, DNA repair, and transcription regulation. In S. pombe, this activity is carried out by HULC, a complex of the Bre1 homologs Brl1 and Brl2 with Rhp6 and Shf1. While H2Bub deposition depends on recruitment of HULC to RNA Pol II by the Paf1 complex (PAF1C), the molecular basis for how PAF1C activates HULC has remained unclear. Using AlphaFold modelling, biochemical reconstitution, and functional assays, we define the architecture of HULC as a flexible 1:1:1:1 assembly in which Shf1 stabilizes an elongated coiled-coil hairpin that brings the RING and Rad6-binding domains into proximity. However, for full stimulation of HULC activity, we find that the HMD domain of the PAF1C subunit Prf1 stimulates ubiquitin transfer through a RING-binding region (RBR) that repositions the RING domains adjacent to Rhp6 in a catalytically competent configuration. These findings reveal an activation mechanism in which transcription-associated Prf1 primes HULC for ubiquitin transfer through the Prf1RBR, revealing a critical regulatory interface for H2B ubiquitination.

molecular biology↗

bioRxiv2024

Testing microbial biomining from asteroidal material onboard the International Space Station

Expanding human space exploration beyond Earths orbit necessitates efficient technologies for self-sustainable acquisition of local resources to overcome unviable resupply missions from Earth. Potential source of materials are asteroids, some of which contain valuable metals, such as platinum group elements. The BioAsteroid experiment, performed onboard the International Space Station, tested the use of microorganisms (bacteria and fungi) to carry out mining of useful elements from asteroidal material (L-chondrite) under microgravity, in support of a long-term human presence in space. The fungus Penicillium simplicissimum, enhanced the mean release of palladium, platinum and other elements from the meteorite material in microgravity, compared to non-biological leaching. However, there was large variability in the results. For many elements, non-biological leaching under microgravity was enhanced compared to terrestrial gravity, while bioleaching was unaffected. Metabolomics results revealed clear patterns that highlight the influence of space conditions on the microbial metabolism, particularly for P. simplicissimum. We identified the presence of carboxylic acids, and molecules of potential biomining and pharmaceutical interest, enhanced in microgravity. These results show a non-trivial effect of microgravity on bioleaching, highlighting the requirement of an optimal combination of microorganism(s), rock substrate, and conditions for successful biomining, both in space and Earth.

microbiology↗

bioRxiv2020

SUV39 SET domains mediate crosstalk of heterochromatic histone marks

The SUV39 class of methyltransferase enzymes deposits histone H3 lysine 9 di- and trimethylation (H3K9me2/3), the hallmark of constitutive heterochromatin. How these enzymes are regulated to mark specific genomic regions as heterochromatic is poorly understood. Clr4 is the sole H3K9me2/3 methyltransferase in the fission yeast S. pombe and recent evidence suggests that ubiquitination of lysine 14 on histone H3 (H3K14ub) plays a key role in H3K9 methylation. However, the molecular mechanism of this regulation and its role in heterochromatin formation remains to be determined. Our structure-function approach shows that the H3K14ub substrate binds specifically and tightly to the catalytic domain of Clr4, and thereby stimulates the enzyme by over 250-fold. Mutations that disrupt this mechanism lead to a loss of H3K9me2/3 and abolish heterochromatin silencing similar to clr4 deletion. Comparison with mammalian SET domain proteins suggests that the Clr4 SET domain harbours a conserved sensor for H3K14ub, which mediates licensing of heterochromatin formation.

molecular biology↗