Proteomic Characterization of a Natural Host–Pathogen Interaction: Repertoire of in Vivo Expressed Bacterial and Host Surface-Associated Proteins

Interactions
between a host and a bacterial pathogen are mediated by cross-talk
between molecules present on, or secreted by, pathogens and host binding-molecules. Identifying proteins involved at this interface
would provide substantial insights into this interaction. Although
numerous studies have examined in vitro models of infection at the
level of transcriptional change and proteomic profiling, there is
virtually no information available on naturally occurring host–pathogen
interactions in vivo. We employed membrane shaving to identify peptide
fragments cleaved from surface-expressed bacterial proteins and also
detected proteins originating from the infected host. We optimized
this technique for media-cultured Corynebacterium pseudotuberculosis, a sheep pathogen, revealing a set of 247 surface proteins. We then
studied a natural host–pathogen interaction by performing membrane
shaving on C. pseudotuberculosis harvested
directly from naturally infected sheep lymph nodes. Thirty-one bacterial
surface proteins were identified, including 13 not identified in culture
media, suggesting that a different surface protein repertoire is expressed
in this hostile environment. Forty-nine host proteins were identified,
including immune mediators and antimicrobial peptides such as cathelicidin.
This novel application of proteolytic shaving has documented sets
of host and pathogen proteins present at the bacterial surface in
an infection of the native host.