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Heme Binding by Corynebacterium diphtheriae HmuT: Function and Heme Environment.

Elizabeth B Draganova1, Neval Akbas1, Seth A Adrian2

  • 1Department of Chemistry, Georgia State University , Atlanta, Georgia 30302-3965, United States.

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|October 20, 2015
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Histidine-136 and Tyrosine-235 are identified as the axial heme ligands in Corynebacterium diphtheriae HmuT, a protein crucial for heme uptake. Mutation of Tyrosine-235 significantly impairs heme transport.

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Area of Science:

  • Microbiology
  • Biochemistry
  • Structural Biology

Background:

  • Corynebacterium diphtheriae requires heme for growth and utilizes a heme uptake (hmu) pathway.
  • Heme is delivered to the ABC transporter HmuUV by the protein HmuT.
  • Understanding HmuT's heme binding is critical for elucidating the heme uptake mechanism.

Purpose of the Study:

  • To determine the axial heme ligands in ferric HmuT.
  • To investigate the roles of conserved heme pocket residues (H136, Y235, M292) in heme binding and transport.
  • To characterize the heme environment within HmuT.

Main Methods:

  • Site-directed mutagenesis of HmuT (H136A, Y235A, M292A).
  • Spectroscopic analyses: UV-visible, resonance Raman, and magnetic circular dichroism.
  • Redox potential measurements and heme-ligand complexation (FeCO, FeF).
  • Hemoglobin utilization assays.

Main Results:

  • Spectroscopic data indicate Histidine-136 and Tyrosine-235 are the axial ligands in ferric HmuT.
  • Mutations H136A and Y235A affect heme reduction potentials, consistent with ligand assignments.
  • FeCO complex analysis provides further evidence for axial ligand identity and heme pocket environment.
  • Y235A mutation significantly impairs heme uptake, highlighting its essential role.

Conclusions:

  • Histidine-136 and Tyrosine-235 serve as the axial ligands for heme in HmuT.
  • Tyrosine-235 is essential for HmuT function in heme uptake.
  • The study provides insights into the heme binding site and its role in heme transport by C. diphtheriae.