Double mutagenesis of a positive charge cluster in the ligand-binding site of the ferric enterobactin receptor, FepA - Newton, Salete Maria Cardozo; Allen, J S; Cao, Z; Qi, Z; Jiang, X; Sprencel, C; Igo, J D; Foster, S B; Payne, M A; Klebba, P E (Proceedings of the National Academy of Sciences of the United States of America, 1997)