1HPB:
reference: The bacterial periplasmic histidine-binding protein. structure/function analysis of the ligand-binding site and comparison with related proteins., Oh BH, Kang CH, De Bondt H, Kim SH, Nikaido K, Joshi AK, Ames GF, J Biol Chem 1994 Feb 11;269(6):4135-43. PMID: 8307974

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