2OK2:
reference: Escherichia coli MutS Tetramerization Domain Structure Reveals That Stable Dimers but Not Tetramers Are Essential for DNA Mismatch Repair in Vivo., Mendillo ML, Putnam CD, Kolodner RD, J Biol Chem. 2007 Jun 1;282(22):16345-54. Epub 2007 Apr 10. PMID: 17426027

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