Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2023

Sulfoxide repair in the respiratory pathogen Haemophilus influenzae – what is the connection between hypochlorite resistance, host immune responses and nutrient acquisition? (93626)

Marufa Nasreen 1 , Remya Purushothaman Nair 1 , Jennifer Hosmer 1 , Ama-Tawiah Essilfie 2 , Alastair McEwan 1 , Ulrike Kappler 1
  1. School of Chemistry & Molecular Biosciences, The University of Queensland, St Lucia, QLD, Australia
  2. QIMR-Berghofer, Herston, Qld

Sulfoxide-damage repair mechanisms are essential for virulence of bacterial pathogens, and strains of the human respiratory pathogen Haemophilus influenzae encode up to three sulfoxide reductases that protect its cell envelope from oxidative damage. Here we have shown that a particularly important role is played by the strictly conserved MsrAB peptide methionine sulfoxide reductase that mediates resistance of Haemophilus influenzae to hypochlorite1. In keeping with this, a Hi2019msrAB knock-out strain was attenuated during infection. MsrAB also affects host immune responses to infection. Infection with a Hi2019msrAB knock-out strain led to specific changes in the expression of host antimicrobial peptides and proteins with antiapoptotic functions1. To better understand how MsrAB mediates these functions, we analysed its enzymatic properties. MsrAB was active with small molecular sulfoxides as well as oxidised calmodulin, and maximal activity was observed at 30°C, a temperature close to that found in the natural niche of H. influenzae, the nasopharynx2. Analyses of differential methionine oxidation identified 29 outer membrane and periplasmic proteins as likely substrates for MsrAB. These included the LldD lactate dehydrogenase which is essential for virulence3, and the lipoprotein eP4 which is involved in NAD and hemin metabolism in H. influenzae. Subsequent experiments showed that H. influenzae MsrAB can repair oxidative damage to methionines in purified eP4 with up to 100% efficiency. Our work links MsrAB to maintenance of different adhesins and essential metabolic processes in H. influenzae, such as NAD metabolism and access to L-lactate, which is a key growth substrate for H. influenzae during infection. We propose that the MsrAB-mediated hypochlorite-resistance and the host immune modulation are indirect effects mediated by enzymes repaired by MsrAB.

  1. Nasreen, M., Dhouib, R., Hosmer, J., Wijesinghe, H. G. S., Fletcher, A., Mahawar, M., Essilfie, A.-T., Blackall, P. J., McEwan, A. G., and Kappler, U. (2020) Peptide methionine sulfoxide reductase from Haemophilus influenzae is required for protection against HOCl and affects the host response to infection. ACS Infect. Dis. 6, 1928-1939
  2. Nasreen, M., Nair, R. P., McEwan, A. G., and Kappler, U. (2022) The Peptide Methionine Sulfoxide Reductase (MsrAB) of Haemophilus influenzae Repairs Oxidatively Damaged Outer Membrane and Periplasmic Proteins Involved in Nutrient Acquisition and Virulence. Antioxidants 11, 1557
  3. Hosmer, J., Nasreen, M., Dhouib, R., Essilfie, A.-T., Schirra, H. J., Henningham, A., Fantino, E., Sly, P., McEwan, A. G., and Kappler, U. (2022) Access to highly specialized growth substrates and production of epithelial immunomodulatory metabolites determine survival of Haemophilus influenzae in human airway epithelial cells. PLoS Pathog 18, e1010209