scholarly journals The src Homology 3-Like Domain of the Diphtheria Toxin Repressor (DtxR) Modulates Repressor Activation through Interaction with the Ancillary Metal Ion-Binding Site

2003 ◽  
Vol 185 (7) ◽  
pp. 2251-2258 ◽  
Author(s):  
John F. Love ◽  
Johanna C. vanderSpek ◽  
John R. Murphy

ABSTRACT The diphtheria toxin repressor (DtxR) is a transition metal ion-activated repressor that acts as a global regulatory element in the control of iron-sensitive genes in Corynebacterium diphtheriae. We recently described (L. Sun, J. C. vanderSpek, and J. R. Murphy, Proc. Natl. Acad. Sci. USA 95:14985-14990, 1998) the isolation and in vivo characterization of a hyperactive mutant of DtxR, DtxR(E175K), that appeared to be constitutively active. We demonstrate here that while DtxR(E175K) remains active in vivo in the presence of 300 μM 2,2′dipyridyl, the purified repressor is, in fact, dependent upon low levels of transition metal ion to transit from the inactive apo form to the active metal ion-bound form of the repressor. Binding studies using 8-anilino-1-naphthalenesulfonic acid suggest that the E175K mutation stabilizes an intermediate of the molten-globule form of the repressor, increasing exposure of hydrophobic residues to solvent. We demonstrate that the hyperactive DtxR(E175K) phenotype is dependent upon an intact ancillary metal ion-binding site (site 1) of the repressor. These observations support the hypothesis that metal ion binding in the ancillary site facilitates the conversion of the inactive apo-repressor to its active, operator-binding conformation. Furthermore, these results support the hypothesis that the C-terminal src homology 3-like domain of DtxR plays an active role in the modulation of repressor activity.

1973 ◽  
Vol 135 (4) ◽  
pp. 785-789 ◽  
Author(s):  
Ian G. Macara ◽  
Terence G. Hoy ◽  
Pauline M. Harrison

Inhibition by Zn2+of iron uptake by apoferritin at very low substrate concentrations is shown to be competitive. It is proposed that Zn2+competes with Fe2+for sites on the protein at which the oxidation of Fe2+is catalysed. Interpretation of titration data suggests there are two independent classes of binding site for Zn2+and several other cations. Sites in one such class are probably on the external surface of the apoferritin molecule. The catalytic binding sites are presumed to be internal and may involve histidine or possibly cysteine as ligands.


2020 ◽  
Vol 142 (13) ◽  
pp. 6365-6374 ◽  
Author(s):  
Lin Frank Song ◽  
Arkajyoti Sengupta ◽  
Kenneth M. Merz

2010 ◽  
Vol 119 (6) ◽  
pp. 3630-3639 ◽  
Author(s):  
Rangam Rajkhowa ◽  
Radhika Naik ◽  
Lijing Wang ◽  
Suzanne V. Smith ◽  
Xungai Wang

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