A type-specific B cell epitope at the apex of Outer surface protein C (OspC) of the Lyme disease spirochete,Borreliella burgdorferi

Broadly protective immunity to the Lyme disease spirochete, Borreliella burgdorferi , is constrained by an overwhelming antibody response against type-specific epitopes on Outer surface protein C (OspC), a homodimeric helix-rich lipoprotein essential for early stages of spirochete dissemination in vertebrate hosts. However, the molecular basis for type-specific immunity has not been fully elucidated. In this report, we produced and characterized an OspC mouse monoclonal antibody, 8C1, that recognizes native and recombinant OspC type A (OspC A ) but not OspC types B or K, and arrests B. burgdorferi motility independent of complement. Epitope mapping by HDX-MS localized 8C1’s epitope to a protruding ridge on the apex of OspC A α-helix 3 (residues 130-150) previously known to be an immunodominant region of the molecule. Alanine scanning pinpointed 8C1’s core binding motif to a solvent exposed patch consisting of residues K 141 H 142 T 143 D 144 . In parallel, analysis of 26 Lyme disease positive serum samples confirmed antibody reactivity with this region of OspC A , with residues E 140 and D 144 as being most consequential. Our results underscore the importance of α-helix 3 as a target of type-specific epitopes on OspC A across mice and humans that should be taken into consideration in Lyme disease vaccine design.