4HU3:
reference: Structures of the catalytic EAL domain of the Escherichia coli direct oxygen sensor., Tarnawski M, Barends TR, Hartmann E, Schlichting I, Acta Crystallogr D Biol Crystallogr. 2013 Jun;69(Pt 6):1045-53. doi:, 10.1107/S0907444913004423. Epub 2013 May 14. PMID: 23695249

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