Electrostatic activation of Escherichia coli methionine repressor.
BACKGROUND
The three-dimensional structure of the Escherichia coli methionine repressor (met repressor) is relatively unperturbed by the binding of its corepressor, S-adenosylmethionine (SAM), and of operator DNA. The positively charged corepressor binds to sites on the repressor remote from the DNA-binding site, and despite the lack of induced structural change is able to raise the affinity for operator DNA by a factor of up to 1000. Neutral corepressor analogues also bind to the repressor, but do not increase operator affinity. These observations suggest that the corepressor effect may be electrostatic.


RESULTS
Using the program DELPHI, we have calculated electrostatic potentials for the repressor and its complexes, and have obtained results consistent with an electrostatic model for repressor activation. The positive potential originating from the corepressor is propagated through the repressor-operator complex, and is significant at DNA phosphate groups buried in the protein-DNA interface. The rank order of calculated electrostatic interaction energies for complexes with SAM, and two closely-related analogues, is in agreement with experimental measurements of the corresponding repressor-operator affinities.


CONCLUSIONS
Long-range (> 10 A) electrostatic interactions between bound corepressor and operator phosphate groups in the repressor-operator complex may be sufficient to explain repressor activation Met repressor could, therefore, be an electrostatically triggered genetic switch.
Phillips
K
K
Department of Biochemistry and Molecular Biology, University of Leeds, UK.
Phillips
S E
SE
D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001483:Base Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006860:Hydrogen Bonding; D008715:Methionine / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D009875:Operator Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000737:chemistry / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism*
D001059:Apoproteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C053317:MetJ protein, E coli; D009838:Oligodeoxyribonucleotides; D012097:Repressor Proteins; C060486:methionine repressor protein, Bacteria; C489220:methionine repressor protein, E coli; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D008715:Methionine