4ISW:
reference: Crystal structure of phosphoramide-phosphorylated thymidylate synthase reveals pSer127, reflecting probably pHis to pSer phosphotransfer., Wilk P, Jarmula A, Ruman T, Banaszak K, Rypniewski W, Ciesla J, Dowiercial A, Rode W, Bioorg Chem. 2013 Nov 21;52C:44-49. doi: 10.1016/j.bioorg.2013.11.003. PMID: 24321279

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