title: Specific purine N7-nitrogens are critical for high affinity binding by the trp repressor.
abstract: We have analysed the interaction of the trp repressor with the trpEDCBA operator using a series of modified trp operator sequences incorporating two isosteric purine analogues that lack N7-nitrogens. Our results suggest that as well as the direct contact between Arg69 and G-9, three additional purine N7-nitrogens, implicated in specific, water-mediated contacts to the repressor, are critical for formation of the high-affinity repressor-operator complex. We conclude that the crystal structure obtained by Otwinowski et al. reflects high-affinity sequence-specific binding of the trp repressor to the trp operator, and that in some cases proteins can use water molecules to extend amino acid side chains in order to derive favorable binding energy in complex formation.
authors.affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02167, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Smith
authors.forename: S B
authors.initials: SB
authors.lastname: Rajur
authors.forename: L W
authors.initials: LW
authors.lastname: McLaughlin
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000737:chemistry; D009875:Operator Regions, Genetic; D011485:Protein Binding; D011687:Purines / Q000737:chemistry / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D013816:Thermodynamics; D014364:Tryptophan / Q000235:genetics; D014867:Water / Q000737:chemistry; D029968:Escherichia coli Proteins
chemical_list: D000469:Alkaline Phosphatase; D001426:Bacterial Proteins; D004247:DNA; D009584:Nitrogen; D011687:Purines; D012097:Repressor Proteins; D014364:Tryptophan; D014867:Water; C027190:TRPR protein, E coli; D029968:Escherichia coli Proteins