Biology subjects

Wassmer, B.

Publications and source records attributed to Wassmer, B..

3 recordsLinked to original sources

bioRxiv2025

(R)-S-Adenosyl-L-methionine hydrolases counter sulfonium epimerisation in thermophilic archaea

S-Adenosyl-L-methionine (SAM) is the second most used enzyme cofactor and vital for numerous cellular reactions such as methylation or polyamine synthesis. While most stereocentres of the biologically active (SS,SC)-SAM are fixed, epimerisation at the methyl sulfonium centre is driven by heat, yielding biologically inactive (RS,SC)-SAM. This SAM diastereomer disturbs SAM-dependent pathways, posing a metabolic threat especially to thermophilic organisms. In vitro analysis shows that SAM hydrolases cleave the biologically inactive (RS,SC)-SAM, thereby constituting to a metabolic salvage pathway. For further analysis of the biological relevance, we characterised two archaeal SAM hydrolases from the thermophilic Sulfolobus acidocaldarius and the halophilic Haloferax volcanii, confirming their selectivity towards (RS,SC)-SAM in vitro. Genetic manipulation in the native hosts supports a significant role of the SAM-hydrolases in decreasing the share of intracellular (RS,SC)-SAM to sustain cellular functions in thermophilic organisms.

biochemistry↗

bioRxiv2025

Archaeal SegAB forms a bipolar structure that promotes chromosome segregation in spherical cells

Archaeal segAB operons are thought to promote chromosome segregation, but their mechanism remains unknown. We employ comparative genomics, structural biology, genetic knockouts, and quantitative cell biology to investigate how SegA and SegB proteins work together to segregate chromosomes in the thermophilic archaeon Sulfolobus acidocaldarius. In vitro, SegB binds a centromeric DNA sequence adjacent to the segAB operon, and in vivo forms a distinct focus on each segregating chromosome. SegA, a ParA-like ATPase, binds DNA non-specifically in vitro and promotes chromosome compaction and segregation in vivo. During division, SegA shifts from chromosome-associated puncta to form a single, elongated figure that runs between separating SegB foci. Late in division, SegA retreats to regions surrounding separated SegB foci. Elongated SegA figures appear in segB knockout cells but no longer lie perpendicular to the division plane. We propose that SegA and SegB interact to form a bipolar, DNA-segregating structure radically different from bacterial ParABS systems.

cell biology↗

bioRxiv2024

New components of the community based DNA-repair mechanism in Sulfolobales

After exposure to UV light, Sulfolobus acidocaldarius cells aggregate in a species-specific manner to exchange DNA and repair double-strand breaks via homologous recombination. The formation of cell-cell interactions is mediated by Ups pili. DNA exchange subsequently occurs through the Ced system, which imports DNA. To identify novel players in these processes, we investigated several genes upregulated after UV exposure by creating in-frame deletion mutants and performing cell aggregation and DNA exchange assays. This led to the identification of two novel components involved in the Ups and Ced systems: UpsC, a minor pilin of the Ups pili, and CedD, a VirD4-like ATPase essential for DNA import. Altogether, these findings provide new insights into the fascinating DNA damage response of Sulfolobales.

microbiology↗