Immunogenic TP0751 fragments

The present application provides methods of stimulating an immune response, such as a protective immune response against Treponema pallidum infection. Such methods utilize fragments of the Tp0751 protein (such as any of SEQ ID NOs: 3-10, those N-terminally truncated from amino acids 1 through 77, 1 through 114, or anywhere in between, e.g., those that start at any amino acid from 78 to 115). In some examples, a Tp0751 protein fragment has a mutated HEXXH site (HEXXH is the wild-type sequence). Also provided are the isolated soluble Tp0751 protein fragments that include a wild-type or mutated HEXXH site, as well as nucleic acids encoding such proteins and kits that include such proteins.