4HAA:
reference: Structure and functional studies of the ribonuclease binase Glu43Ala/Phe81Ala mutant., Mitkevich VA, Schulga AA, Trofimov AA, Dorovatovskii PV, Goncharuk DA, Tkach EN, Makarov AA, Polyakov KM, Acta Crystallogr D Biol Crystallogr. 2013 Jun;69(Pt 6):991-6. doi:, 10.1107/S0907444913004046. Epub 2013 May 11. PMID: 23695243

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