5YCU:
reference: A five-residue motif for the design of domain swapping in proteins., Nandwani N, Surana P, Negi H, Mascarenhas NM, Udgaonkar JB, Das R, Gosavi S, Nat Commun. 2019 Jan 28;10(1):452. doi: 10.1038/s41467-019-08295-x. PMID: 30692525

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