Cardiolipins: elucidating their diversity, biosynthesis and role in the membrane adaptation of pathogens towards environmental stress.

• Applicant: Dr. Marten Exterkate
• Subject Area: Biochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 557049601

Cardiolipins are structurally unique phospholipids that are universally present in energy-transducing membranes in all domains of life. In general, cardiolipins exist out of 4 hydrophobic bulky lipid tails linked to a small hydrophilic headgroup, which give rise to a characteristic cone-like shape that is associated with membrane curvature (e.g., cell poles and division site). The most common and well-studied cardiolipin is 1,3-bis(sn-3’-phosphatidyl)-sn-glycerol, or simply glycerol-di-phosphatidyl-cardiolipin (Gro-DPCL), of which the headgroup contains two phosphates that are linked by a glycerol. Interestingly, in bacteria and archaea other cardiolipin species have been identified as well, with a wide variety of different headgroups, including multiple sugars, additional sulfate groups and amino acids. However, hardly anything is known about their synthesis, under which conditions they are produced, and what their cellular functions are. As a first step towards answering these questions, we previously identified, purified and characterized a cardiolipin synthase from Methanospirillum hungatei (MhCls), for which a remarkable substrate promiscuity was observed. By supplying different substrates, a wide variety of phospholipids and cardiolipins could be synthesized, indicating that a single enzyme type could be responsible for the synthesis of various different cardiolipin species. Furthermore, incidental reports have shown that some cardiolipins fluctuate upon changes in environmental conditions (e.g., osmotic shock, nutrient depletion, antibiotics), suggesting a role in the membrane adaptation towards environmental stress. Interestingly, in these processes the unique chemistry of the head group seems to play a pivotal role, which makes the structurally diverse family of cardiolipins an interesting target to further explore. In this project, we propose to: (1.) study MhCls as a model for cardiolipin synthesis to further unravel the substrate promiscuity and enzymatic mechanism at the molecular level. (2.) extent our research on the synthesis of different cardiolipins, by the identification, purification and characterization of other (putative) cardiolipin synthases. We will specifically focus on the production of glycol-cardiolipins that contain only one phosphate-moiety and a sugar headgroup. (3.) systematically address the cardiolipin response towards a variety of environmental stress conditions in bacterial pathogens and investigate the potential role of cardiolipins in the innate immune response.

• DFG Programme: Research Grants