5SY9:
reference: Short Carboxylic Acid-Carboxylate Hydrogen Bonds Can Have Fully Localized Protons., Lin J, Pozharski E, Wilson MA, Biochemistry. 2016 Dec 30. doi: 10.1021/acs.biochem.6b00906. PMID: 27989121

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