1QMP:
reference: Phosphorylated aspartate in the structure of a response regulator protein., Lewis RJ, Brannigan JA, Muchova K, Barak I, Wilkinson AJ, J Mol Biol 1999 Nov 19;294(1):9-15. PMID: 10556024

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