The Role of Gram-Positive Surface Proteins in Bacterial Niche- and Host-Specialization

An atlas of human vector-borne microbe interactions reveals pathogenicity mechanisms

Vector-borne diseases are a leading cause of death worldwide and pose a substantial unmet medical need. Pathogens binding to host extracellular proteins (the "exoproteome") represents a crucial interface in the etiology of vector-borne disease. Here, we used bacterial selection to elucidate host-microbe interactions in high throughput (BASEHIT)-a technique enabling interrogation of microbial interactions with 3,324 human exoproteins-to profile the interactomes of 82 human-pathogen samples, including 30 strains of arthropod-borne pathogens and 8 strains of related non-vector-borne pathogens. The resulting atlas revealed 1,303 putative interactions, including hundreds of pairings with potential roles in pathogenesis, including cell invasion, tissue colonization, immune evasion, and host sensing. Subsequent functional investigations uncovered that Lyme disease spirochetes recognize epidermal growth factor as an environmental cue of transcriptional regulation and that conserved interactions between intracellular pathogens and thioredoxins facilitate cell invasion. In summary, this interactome atlas provides molecular-level insights into microbial pathogenesis and reveals potential host-directed targets for next-generation therapeutics.

Quantification of Adaptive Immune Responses Against Protein-Binding Interfaces in the Streptococcal M1 Protein

Bacterial or viral antigens can contain subdominant protein regions that elicit weak antibody responses upon vaccination or infection although there is accumulating evidence that antibody responses against subdominant regions can enhance the protective immune response. One proposed mechanism for subdominant protein regions is the binding of host proteins that prevent antibody production against epitopes hidden within the protein binding interfaces. Here, we used affinity purification combined with quantitative mass spectrometry (AP-MS) to examine the level of competition between antigen-specific antibodies and host-pathogen protein interaction networks using the M1 protein from Streptococcus pyogenes as a model system. As most humans have circulating antibodies against the M1 protein, we first used AP-MS to show that the M1 protein interspecies protein network formed with human plasma proteins is largely conserved in naïve mice. Immunizing mice with the M1 protein generated a time-dependent increase of anti-M1 antibodies. AP-MS analysis comparing the composition of the M1-plasma protein network from naïve and immunized mice showed significant enrichment of 292 IgG peptides associated with 56 IgG chains in the immune mice. Despite the significant increase of bound IgGs, the levels of interacting plasma proteins were not significantly reduced in the immune mice. The results indicate that the antigen-specific polyclonal IgG against the M1 protein primarily targets epitopes outside the other plasma protein binding interfaces. In conclusion, this study demonstrates that AP-MS is a promising strategy to determine the relationship between antigen-specific antibodies and host-pathogen interaction networks that could be used to define subdominant protein regions of relevance for vaccine development.

Comparative Surfaceome Analysis of Clonal Histomonas meleagridis Strains with Different Pathogenicity Reveals Strain-Dependent Profiles

Histomonas meleagridis, a poultry-specific intestinal protozoan parasite, is histomonosis’s etiological agent. Since treatment or prophylaxis options are no longer available in various countries, histomonosis can lead to significant production losses in chickens and mortality in turkeys. The surfaceome of microbial pathogens is a crucial component of host–pathogen interactions. Recent proteome and exoproteome studies on H. meleagridis produced molecular data associated with virulence and in vitro attenuation, yet the information on proteins exposed on the cell surface is currently unknown. Thus, in the present study, we identified 1485 proteins and quantified 22 and 45 upregulated proteins in the virulent and attenuated strains, respectively, by applying cell surface biotinylation in association with high-throughput proteomic analysis. The virulent strain displayed upregulated proteins that could be linked to putative virulence factors involved in the colonization and establishment of infection, with the upregulation of two candidates being confirmed by expression analysis. In the attenuated strain, structural, transport and energy production proteins were upregulated, supporting the protozoan’s adaptation to the in vitro environment. These results provide a better understanding of the surface molecules involved in the pathogenesis of histomonosis, while highlighting the pathogen’s in vitro adaptation processes.