So Long Llamas: Structure of Activated Angiotensin Receptor Stabilized by a Synthetic Nanobody

Nanobodies are single‐domain antibody fragments that are derived from camelids and used extensively as research tools. Despite their usefulness, traditional immunization‐based approaches for generating nanobodies have proven ineffective for producing nanobody binders to some antigen targets. To overcome this, we bypassed the requirement of camelids by creating a synthetic in vitro library of nanobodies. Using this library, we developed a nanobody which stabilizes the active state of a GPCR, angiotensin II type 1 receptor (AT1R). AT1R is a critical regulator of cardiovascular function and our collaborator’s previous nanobody discovery efforts using camelids were unsuccessful. Our synthetic conformational nanobody, Nb.AT110i1, allowed us to determine the crystal structure of active‐state human AT1R bound to an analog of its endogenous hormone angiotensin II. This structure provides detailed insight into hormone binding and may lead to new therapeutics. It also contributes a remarkably complete explanation for receptor activation.