Seizure 6-like protein is a protein that in humans is encoded by the SEZ6L gene. SEZ6L (Seizure 6-Like protein; also BSRP-B in rodent) is a 200 kDa member of the SEZ6 family of proteins. It is expressed in the plasma membrane and ER of CNS neurons and lung bronchiolar epithelium, and likely regulates PKC alpha activation. Mature human SEZ6L is a 996 amino acid (aa) type I transmembrane protein. It contains a 930 aa extracellular domain (ECD) (aa 29-958) plus a 45 aa cytoplasmic tail. The ECD shows three CUB domains and five short consensus repeats (SCRs). There are multiple isoforms possible for SEZ6L. One shows a deletion of aa 933-943, and a second shows the same deletion coupled to a Thr substitution for aa 803-867. A third isoform contains a Leu substitution for aa 867-943. An alternative start site is reported at Met228. This start site may occur individually, or be accompanied by a deletion of aa 932-944, the same deletion of aa 932-944 coupled to a Thr substitution for aa 803-867, or a duel deletion of aa 869-945 and 1016-1024. Over aa 29-958, human BSRP-B is 80% aa identical to mouse BSRP-B.