BRSK2 (BR serine/threonine kinase 2), also known as SAD1, STK29 or PEN11B, is a 736 amino acid protein that contains one protein kinase domain and is preferentially expressed in brain and testis. One of several members of the Ser/Thr protein kinase family, BRSK2 uses magnesium as a cofactor to catalyze the ATP-dependent phosphorylation of target proteins and is thought to be involved in microtubule assembly, neuronal polarization and synaptic development. Additionally, BRSK2 may function as an autoantigen involved in small-cell lung cancer-associated limbic encephalitis. Five isoforms of BRSK2 exist due to alternative splicing events.