Structure of a transmission blocking antibody in complex with Outer surface protein A from the Lyme disease spirochete, Borreliella burgdorferi

Abstract

Abstract319‐44 is a human monoclonal antibody capable of passively protecting mice against tick‐mediated infection with Borreliella burgdorferi, the bacterial genospecies responsible for Lyme disease in North America. In vitro, 319‐44 has complement‐dependent borreliacidal activity and spirochete agglutinating properties. Here, we report the 2.2 Å‐resolution crystal structure of 319‐44 Fab fragments in complex with Outer surface protein A (OspA), the ~30 kDa lipoprotein that was the basis of the first‐generation Lyme disease vaccine approved in the United States. The 319‐44 epitope is focused on OspA β‐strands 19, 20, and 21, and the loops between β‐strands 16‐17, 18‐19, and 20‐21. Contact with loop 20‐21 explains competition with LA‐2, the murine monoclonal antibody used to estimate serum borreliacidal activities in the first‐generation Lyme disease vaccine clinical trials. A high‐resolution B‐cell epitope map of OspA will accelerate structure‐based design of second generation OspA‐based vaccines.