Streptococcus pneumoniae requires iron for its viability and expresses two membrane proteins that bind haemoglobin and haem

Abstract

Streptococcus pneumoniae, a human pathogen bacterium, can support its growth using haemoglobin (Hb) and haem as sole iron sources, but not when holo-transferrin or holo-lactoferrin is supplied. For this reason, it is easy to think that the principal iron sources for this pathogen inside humans are Hb and haem. Unfortunately, the mechanism has been poorly studied. The findings presented in this study are the first efforts that attempted to explain the mechanism involved in iron acquisition of this pathogen. This pathogen was capable of supporting its viability when iron sources such as Hb or haem were supplied. Membranes of S. pneumoniae were separated and their respective proteins were solubilized in order to be purified by haem-affinity chromatography. This strategy allowed us to purify seven membrane proteins. An experiment of competence with haem and iron showed two potential haem and Hb-binding proteins. Their Hb-binding function was confirmed by overlay assay using Hb and their respective identities were obtained by mass spectrometry. Then by amino acid alignment analysis, the motif involved in binding of Hb or haem was revealed. These results are the first findings that attempt to explain the mechanisms developed by S. pneumoniae to acquire iron from Hb or haem in the host, which could allow a better understanding of the biology of this bacterium.