Covalent bonding of heme to protein prevents heme capture by nontypeable Haemophilus influenzae

Abstract

Nontypeable Haemophilus influenzae (NTHi) are Gram‐negative pathogens that contribute to a variety of diseases, including acute otitis media and chronic obstructive pulmonary disease. As NTHi have an absolute requirement for heme during aerobic growth, these bacteria have to scavenge heme from their human hosts. These heme sources can range from free heme to heme bound to proteins, such as hemoglobin. To test the impact of heme structural factors on heme acquisition by NTHi, we prepared a series of heme sources that systematically vary in heme exposure and covalent binding of heme to peptide/protein and tested the ability of NTHi to use these sources to support growth. Results from this study suggest that NTHi can utilize protein‐associated heme only if it is noncovalently attached to the protein.

In Vitro Anti-NTHi Activity of Haemophilin-Producing Strains of Haemophilus haemolyticus

“…NTHi is particularly susceptible to heme restriction as it lacks the necessary enzymes for its synthesis and relies solely on scavenging heme from the host, either in the form of free heme or bound to host carrier molecules [16,[21][22][23]. Evidence from our laboratory suggests that closely related commensals may present a competitive challenge for heme acquisition in the URT.…”

The heme auxotroph Caenorhabditis elegans can cleave the thioether bonds of c‐type cytochromes

“…Heme is not only essential for life but also an expensive molecule to synthesize. Organisms go to great lengths to regulate its production but also to reuse it when possible and acquire it from their environment, as seen, for example, with bacterial pathogens and their heme acquisition systems . Here, we conclusively show that organisms like the nematode C. elegans , have developed specialized systems to extract heme even when it is covalently bound, like in cytochromes c .…”

“…Organisms go to great lengths to regulate its production but also to reuse it when possible and acquire it from their environment, as seen, for example, with bacterial pathogens and their heme acquisition systems [8,36,37]. Here, we conclusively show that organisms like the nematode C. elegans, have developed specialized systems to extract heme even when it is covalently bound, like in cytochromes c. This observation, which contrasts with the recently reported failure of H. influenzae to capture heme from c-type cytochromes [8], has the potential to lead to the discovery of an entirely new class of hemehandling proteins which are not necessarily limited to heme auxotrophs. In the case of parasitic protists, like T. brucei, which also acquire their heme externally, such a discovery could be particularly significant as it might identify a new target for the development of compounds which could limit the growth of these organisms.…”

Panel 7 – Pathogenesis of otitis media – a review of the literature between 2015 and 2019

“…In addition to soluble heme, NTHI are able to extract heme from heme-binding proteins in the extracellular environment. Work by Sgheiza et al found that while NTHi are able to extract and use heme that is non-covalently bound to proteins, NTHI are unable to efficiently acquire heme that has been covalently bound to protein [59].…”