The host range, or tropism, of pathogen virulence factors is a key determinant of infection. A
detailed understanding of host and pathogen mutations that control species tropism is required in
order to assess the risk of future zoonotic disease outbreaks, improve animal infection models, and
design new therapeutics that take advantage of host specificity.
The objective of this proposal is to define barriers to cross-species activity in bacterial
virulence factors at high resolution, leveraging staphylococcal exfoliative toxins as a study system.
Exfoliative toxins encoded by pathogenic bacteria in the genus Staphylococcus cause life-
threatening skin diseases including staphylococcal scalded skin syndrome and bullous impetigo
characterized by widespread blistering and damage to the epidermis. Exfoliative toxins are
proteases that act by selectively cleaving the skin desmosomal cadherin desmoglein-1, leading to
loss of epidermal barrier function and blister formation. Our central hypothesis is that virulence
factor activity is dependent on genetic compatibilities between hosts and pathogens, and that
interrogating these compatibilities will uncover specific barriers to host tropism. In preliminary work,
we found that genes encoding desmoglein-1 have undergone rapid evolution and repeated natural
selection across non-human primates within a small protein surface sufficient to restrict toxin activity.
We have also developed tractable in vitro assays to measure toxin cleavage of recombinant
desmglein-1 from various host species.
The Specific Aims of this proposal are to 1) generate a high-resolution map of mutations in
desmoglein-1 that restrict toxin tropism, and 2) test how toxin mutations at the desmoglein-1 binding
interface contribute to host tropism. In Aim 1 we will perform combinatorial mutagenesis of the toxin
recognition surface in desmoglein-1 to produce a genetic map defining the barriers of host
recognition. In Aim 2 we will apply structural and biochemical approaches to resolve the desmoglein-
exfoliative toxin binding interface combined with genetics to assess how toxin mutations at this
surface control host tropism. Collectively this proposal will establish a framework to define genetic
barriers to bacterial infections at high-resolution, applied towards the goal of anticipating and
preventing future disease outbreaks.