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Monothiol glutaredoxins function in storing and transporting [Fe2S2] clusters assembled on IscU scaffold proteins
Priyanka Shakamuri1, Bo Zhang, Michael K Johnson
1Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia, Athens, Georgia 30602, USA.
Journal of the American Chemical Society
|September 12, 2012
Summary
Molecular chaperones HscA and HscB significantly accelerate iron-sulfur cluster transfer from IscU to Grx5, essential for bacterial iron-sulfur cluster assembly. This highlights the necessity of these co-chaperones for efficient in vitro studies.
Area of Science:
- Biochemistry
- Molecular Biology
- Microbiology
Background:
- Iron-sulfur (Fe-S) clusters are vital cofactors for numerous proteins.
- The iron-sulfur cluster (ISC) assembly machinery in bacteria involves scaffold proteins like IscU and molecular co-chaperones HscA and HscB.
- IscU serves as a primary scaffold for Fe-S cluster assembly, with HscA and HscB facilitating ATP-dependent cluster transfer.
Purpose of the Study:
- To investigate the role of molecular co-chaperones HscA and HscB in the transfer of Fe-S clusters from IscU to apo-Grx5.
- To quantify the rate enhancement of Fe-S cluster transfer mediated by HscA/HscB/Mg-ATP.
Main Methods:
- Utilized circular dichroism (CD) spectroscopy to monitor [Fe(2)S(2)](2+) cluster transfer.
- Compared cluster transfer rates from [Fe(2)S(2)](2+)-bound IscU to apo-Grx5 in the absence and presence of HscA/HscB/Mg-ATP.
- Determined the second-order rate constant for the transfer process.
Main Results:
- Observed a 700-fold enhancement in the rate of [Fe(2)S(2)](2+) cluster transfer in the presence of HscA/HscB/Mg-ATP.
- Calculated a second-order rate constant of 20,000 M⁻¹ min⁻¹ at 23 °C for the HscA/HscB-mediated transfer.
- Demonstrated that HscA and HscB are indispensable for efficient ATP-dependent [Fe(2)S(2)](2+) cluster transfer from IscU to Grx5.
Conclusions:
- HscA and HscB are essential for efficient ATP-dependent [Fe(2)S(2)](2+) cluster transfer from IscU to Grx5.
- Monothiol glutaredoxins (Grx's) likely play a role in storing and transporting Fe-S clusters assembled on IscU.
- In vitro studies of [Fe(2)S(2)](2+)-IscU cluster transfer require the inclusion of the HscA/HscB co-chaperone system for accurate interpretation.
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