Direct Mapping of Polyclonal Epitopes in Serum by HDX-MS

Elucidating the interactions that
drive antigen recognition is
central to understanding antibody-mediated protection and is vital
for the rational design of immunogens. Often, structural knowledge
of epitopes targeted by antibodies is derived from isolated studies
of monoclonal antibodies, for which numerous structural techniques
exist. In contrast, there are very few approaches capable of mapping
the full scope of antigen surfaces targeted by polyclonal sera through
the course of a natural antibody response. Here, we develop an approach
using immobilized antigen coupled to hydrogen/deuterium exchange with
mass spectrometry (HDX-MS) to probe epitope targeting in the context
of the fully native serum environment. Using the well-characterized Staphylococcal enterotoxin B (SEB) as a model system, we
show that complex combinations of epitopes can be detected and subtle
differences across different antisera can be discerned. This work
reveals new insight into how neutralizing antibodies and antisera
target SEB and, more importantly, establishes a novel method for directly
mapping the epitope landscape of polyclonal sera.