3H9R:
reference: Structure of the Bone Morphogenetic Protein Receptor ALK2 and Implications for Fibrodysplasia Ossificans Progressiva., Chaikuad A, Alfano I, Kerr G, Sanvitale CE, Boergermann JH, Triffitt JT, von Delft F, Knapp S, Knaus P, Bullock AN, J Biol Chem. 2012 Oct 26;287(44):36990-8. doi: 10.1074/jbc.M112.365932. Epub 2012, Sep 12. PMID: 22977237

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