The Exoproteome and Surfaceome of Toxigenic Corynebacterium diphtheriae 1737 and Its Response to Iron Restriction and Growth on Human Hemoglobin

Toxin-producing Corynebacterium
diphtheriae strains are the etiological agents of
the severe upper respiratory
disease, diphtheria. A global phylogenetic analysis revealed that
biotype gravis is particularly lethal as it produces diphtheria toxin
and a range of other virulence factors, particularly when it encounters
low levels of iron at sites of infection. To gain insight into how
it colonizes its host, we have identified iron-dependent changes in
the exoproteome and surfaceome of C. diphtheriae strain 1737 using a combination of whole-cell fractionation, intact
cell surface proteolysis, and quantitative proteomics. In total, we
identified 1414 of the predicted 2265 proteins (62%) encoded by its
reference genome. For each protein, we quantified its degree of secretion
and surface exposure, revealing that exoproteases and hydrolases predominate
in the exoproteome, while the surfaceome is enriched with adhesins,
particularly DIP2093. Our analysis provides insight into how components
in the heme-acquisition system are positioned, showing pronounced
surface exposure of the strain-specific ChtA/ChtC paralogues and high
secretion of the species-conserved heme-binding HtaA protein, suggesting
it functions as a hemophore. Profiling the response of the exoproteome
and surfaceome after microbial exposure to human hemoglobin and iron
limitation reveals potential virulence factors that may be expressed
at sites of infection. Data are available via ProteomeXchange with
identifier PXD051674.