Mn(II) binding by the anthracis repressor from Bacillus anthracis.
The anthracis repressor (AntR) is a manganese-activated transcriptional regulator from Bacillus anthracis and is a member of the diphtheria toxin repressor (DtxR) family of proteins. In this paper, we characterize the Mn(II) binding and protein dimerization state using a combination of continuous wave (cw) and pulsed EPR methods. Equilibrium metal binding experiments showed that AntR binds 2 equivalents of Mn(II) with positive cooperativity and apparent dissociation constants of 210 and 16.6 microM. AntR showed sub-millisecond Mn(II) on-rates as measured using stopped-flow EPR. The kinetics of Mn(II) dissociation, measured by displacement with Zn(II), was biphasic with rate constants of 35.7 and 0.115 s(-1). Variable-temperature parallel and perpendicular mode cw EPR spectra showed no evidence of a spin-exchange interaction, suggesting that the two Mn(II) ions are not forming a binuclear cluster. Finally, size exclusion chromatography and double electron-electron resonance EPR demonstrated that AntR forms a dimer in the absence of Mn(II). These results provide insights into the metal activation of AntR and allow a comparison with related DtxR proteins.
Sen
K Ilker
KI
Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA.
Sienkiewicz
Andrzej
A
Love
John F
JF
vanderSpek
Johanna C
JC
Fajer
Piotr G
PG
Logan
Timothy M
TM
D001408:Bacillus anthracis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C075586:DtxR protein, Corynebacterium diphtheriae; C433792:MntR protein, bacteria; D012097:Repressor Proteins; D008345:Manganese