3B4V:
reference: The structure of FSTL3.activin A complex. Differential binding of N-terminal domains influences follistatin-type antagonist specificity., Stamler R, Keutmann HT, Sidis Y, Kattamuri C, Schneyer A, Thompson TB, J Biol Chem. 2008 Nov 21;283(47):32831-8. Epub 2008 Sep 2. PMID: 18768470

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