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Iron chelation properties of an extracellular siderophore exochelin MN.

Publication ,  Journal Article
Dhungana, S; Miller, MJ; Dong, L; Ratledge, C; Crumbliss, AL
Published in: Journal of the American Chemical Society
June 2003

The coordination chemistry of an extracellular siderophore produced by Mycobacterium neoaurum, exochelin MN (ExoMN), is reported along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titration techniques. Exochelin MN is of particular interest as it can efficiently transport iron into pathogenic M. leprae, which is responsible for leprosy, in addition to its own parent cells. The Fe(III) coordination properties of ExoMN are important with respect to understanding the Fe(III) acquisition and uptake mechanism in pathogenic M. leprae, as the siderophores from this organism are very difficult to isolate. Exochelin MN has two hydroxamic acid groups and an unusual threo-beta-hydroxy-l-histidine available for Fe(III) chelation. The presence of threo-beta-hydroxy-l-histidine gives rise to a unique mode of Fe(III) coordination. The pK(a) values for the two hydroxamic acid moieties, the histidine imidazole ring and the alkylammonium groups on ExoMN, correspond well with the literature values for these moieties. Proton-dependent Fe(III)- and Fe(II)-ExoMN equilibrium constants were determined using a model involving sequential protonation of the Fe(III)- and Fe(II)-ExoMN complexes. These data were used to develop a model whereby deprotonation reactions on the surface of the complex in the second coordination shell result in first coordination shell isomerization. The overall formation constants were calculated: log beta(110) = 39.12 for Fe(III)-ExoMN and 16.7 for Fe(II)-ExoMN. The calculated pFe value of 31.1 is one of the highest among all siderophores and their synthetic analogues and indicates that ExoMN is thermodynamically capable of removing Fe(III) from transferrin. The E(1/2) for the Fe(III)ExoMN/Fe(II)ExoMN(-) couple was determined to be -595 mV from quasi-reversible cyclic voltammograms at pH = 10.8, and the pH-dependent E(1/2) profile was used to determine the Fe(II)-ExoMN protonation constants.

Duke Scholars

Published In

Journal of the American Chemical Society

DOI

EISSN

1520-5126

ISSN

0002-7863

Publication Date

June 2003

Volume

125

Issue

25

Start / End Page

7654 / 7663

Related Subject Headings

  • Spectrophotometry, Ultraviolet
  • Potentiometry
  • Peptides, Cyclic
  • Mycobacterium
  • Kinetics
  • Iron Chelating Agents
  • Hydrogen-Ion Concentration
  • General Chemistry
  • Ferrous Compounds
  • Ferric Compounds
 

Citation

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ICMJE
MLA
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Dhungana, S., Miller, M. J., Dong, L., Ratledge, C., & Crumbliss, A. L. (2003). Iron chelation properties of an extracellular siderophore exochelin MN. Journal of the American Chemical Society, 125(25), 7654–7663. https://doi.org/10.1021/ja029578u
Dhungana, Suraj, Marvin J. Miller, Li Dong, Colin Ratledge, and Alvin L. Crumbliss. “Iron chelation properties of an extracellular siderophore exochelin MN.Journal of the American Chemical Society 125, no. 25 (June 2003): 7654–63. https://doi.org/10.1021/ja029578u.
Dhungana S, Miller MJ, Dong L, Ratledge C, Crumbliss AL. Iron chelation properties of an extracellular siderophore exochelin MN. Journal of the American Chemical Society. 2003 Jun;125(25):7654–63.
Dhungana, Suraj, et al. “Iron chelation properties of an extracellular siderophore exochelin MN.Journal of the American Chemical Society, vol. 125, no. 25, June 2003, pp. 7654–63. Epmc, doi:10.1021/ja029578u.
Dhungana S, Miller MJ, Dong L, Ratledge C, Crumbliss AL. Iron chelation properties of an extracellular siderophore exochelin MN. Journal of the American Chemical Society. 2003 Jun;125(25):7654–7663.
Journal cover image

Published In

Journal of the American Chemical Society

DOI

EISSN

1520-5126

ISSN

0002-7863

Publication Date

June 2003

Volume

125

Issue

25

Start / End Page

7654 / 7663

Related Subject Headings

  • Spectrophotometry, Ultraviolet
  • Potentiometry
  • Peptides, Cyclic
  • Mycobacterium
  • Kinetics
  • Iron Chelating Agents
  • Hydrogen-Ion Concentration
  • General Chemistry
  • Ferrous Compounds
  • Ferric Compounds