2PQE:
reference: Restricted backbone conformational and motional flexibilities of loops containing peptidyl-proline bonds dominate the enzyme activity of staphylococcal nuclease., Shan L, Tong Y, Xie T, Wang M, Wang J, Biochemistry. 2007 Oct 16;46(41):11504-13. Epub 2007 Sep 22. PMID: 17887731

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