A novel ECF-type transporter promotes heme acquisition in Staphylococcus lugdunensis to overcome nutritional limitation

• Applicant: Professor Dr. Simon Heilbronner
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429484415

During invasive infection of pathogens, the host does implement active limitation of essential nutrients such as iron ions within the tissues and body fluids. This "nutritional immunity" does effectively limit bacterial proliferation and is an important part of the innate immune system. Bacterial pathogens such as the staphylococcus species S. aureus and S. lugdunensis possess iron-responsive surface determinant (isd) loci. Isd systems contain cell wall-anchored proteins, a membrane transporter and cytosolic proteins allowing heme to be extracted from hemoglobin, to be transported into the cytoplasm, and to be degraded to release the iron ion. As such, Isd systems are hallmarks of bacterial pathogens allowing to overcome “nutritional immunity”.We investigated the Isd system of S. lugdunensis and found that a mutant lacking the heme specific ABC transporter (IsdEFL) did not lose its ability to use heme as an iron source. We identified a novel ABC transporter (Lha) and mutants lacking this transporter showed a strongly reduced ability to thrive on heme as an iron source. Lha belongs to the energy coupling factor-type (ECF) of ABC transporters. The substrate-specific components of ECF transporters are highly hydrophobic membrane proteins with extraordinary affinity towards their substrate. ECF transporters represent micronutrient uptake systems and only a hand full of ligands are known. Our data indicate that Lha is specific for heme, identifying a novel substrate and making it the first ECF transporter putatively involved in overcoming host innate immune strategies. Using biochemical techniques, we will investigate whether Lha possesses the expected high affinity to heme and whether it outperforms the conventional heme-specific lipoprotein IsdE. In a conventional Isd system, surface-anchored proteins extract heme from hemoproteins and funnel it to the membrane transporter. This raises the question why a high-affinity membrane transporter is needed in addition. To address this, we will investigate whether Lha is functionally dependent on the Isd system or whether it is an autonomous heme acquisition system. We hypothesize that the affinity of Lha towards heme is high enough to extract heme from low-abundance hemoproteins such as cytochromes or myoglobin. Thereby it could represent an Isd-independent pathway to expand the hemoprotein substrate range. To challenge this hypothesis we will investigate heme transfer between host hemoproteins and Lha as well as between LhaS and the Isd proteins on the biochemical level. Simultaneously, we will express the Lha system in the surrogate host Staphylococcus carnosus (lacking other Isd proteins) and create isogenic isd deletion mutations in S. lugdunensis. This will allow identifying whether Lha is functionally dependent on the Isd proteins on the physiological level.

• DFG Programme: Research Grants
• International Connection: Netherlands
• Cooperation Partner: Professor Dr. Dirk Slotboom, Ph.D.