Generation and characterization of a laforin nanobody inhibitor

Mutations in the gene encoding the glycogen phosphatase laforin result in the fatal childhood epilepsy Lafora disease (LD). A cellular hallmark of LD is cytoplasmic, hyper-phosphorylated, glycogen-like aggregates called Lafora bodies (LBs) that form in nearly all tissues and drive disease progression. Additional tools are needed to define the cellular function of laforin, understand the pathological role of laforin in LD, and determine the role of glycogen phosphate in glycogen metabolism. We present the generation and characterization of laforin nanobodies. We identify multiple classes of specific laforin-binding nanobodies and determine their binding epitopes using hydrogen deuterium exchange (HDX) mass spectrometry. Further, one family of nanobodies is identified that serves as an inhibitor of laforin catalytic activity. The laforin nanobodies are an important set of tools that open new avenues to define unresolved questions.