1BTE:
reference: Three-finger toxin fold for the extracellular ligand-binding domain of the type II activin receptor serine kinase., Greenwald J, Fischer WH, Vale WW, Choe S, Nat Struct Biol 1999 Jan;6(1):18-22. PMID: 9886286

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).