Exploration of physiological functions of the cell fusogen Fusexin1 in Archaea

• Applicant: Professorin Dr. Sonja Verena Albers
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561072054

Cell-cell fusion is essential for sexual reproduction where the merger of gametes initiates the development of a new organism in eukaryotes. Our groups discovered and developed basic molecular cell biological mechanisms required for cell motility and cell division in archaea (Albers) and the first proteins (fusogens) that are essential and sufficient to fuse cells during development in eukaryotes and more recently cell fusogens in archaea (Podbilewicz). These fusogenic proteins are part of a superfamily of structurally conserved fusogens in archaea, nematodes, enveloped viruses, plants, protists and invertebrates. We found that these fusogens in archaea that we named Fusexin1 (Fsx1) are structurally related to eukaryotic and viral class II fusogens (fusexins). The genes encoding for Fsx1 are contained in integrated mobile elements (IMEs) in different cultivated haloarchaea and Fsx1 protein can fuse eukaryotic cells. However, Fsx1 in vivo activities are unknown. Transformation, conjugation and transduction can mediate DNA transfer in bacteria and archaea. The function of Fsx1 in archaea may uncover a fourth mechanism of Horizontal Gene Transfer (HGT) in prokaryotes that relies on cell fusion and could also explain how outer membrane vesicles fuse. This is significant because it is known that HGT is a very abundant process in prokaryotes with potential implications to biomedicine and evolutionary biology. Here, we propose that Fsx1 encoding genes in archaea that are present in IMEs, have activities required for a novel type of HGT. Our main goal is to uncover the function of cell fusion in archaea and whether Fsx1 in archaea participates in HGT. To determine the function(s) of Fsx1 in haloarchaea we will use multidisciplinary approaches including state-of-the-art cell biological and molecular genetics in archaea. In our preliminary results we have generated fsx1 deletion mutants in Haloferax sp. Q22 and a strain with ectopic expression of fsx1 in Haloferax volcanii to determine the loss-of-function and gain-of-function phenotypes in archaea. To study the molecular mechanisms used by Fsx1 in heterologous systems, we will use cell-cell, virus-cell and in vitro reconstitution assays in proteoliposomes. We aim to discover new cofactors, investigate the functions of novel protein interactions, and whether Fsx1 mediates a cell fusion-dependent process in archaea to induce HGT. We will investigate whether Fsx1 mediates a cell fusion-dependent HGT in archaea. The proposed studies of Fsx1, will change paradigms of HGT in prokaryotes. Understanding how cells fuse in archaeal systems will be a breakthrough in biology with broad implications in mechanisms of HGT, sexual reproduction and evolution of cell fusion.

• DFG Programme: Research Grants
• International Connection: Israel
• Partner Organisation: The Israel Science Foundation
• Cooperation Partner: Professor Dr. Benjamin Podbilewicz