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Two Fe-S clusters catalyze sulfur insertion by radical-SAM methylthiotransferases
Farhad Forouhar1, Simon Arragain, Mohamed Atta
1Northeast Structural Genomics Consortium, New York, New York, USA.
Nature Chemical Biology
|April 2, 2013
Summary
This study reveals how enzymes MiaB and RimO catalyze the creation of vital carbon-sulfur bonds. A novel sulfation mechanism is proposed, where a second iron-sulfur cluster acts as a catalytic site, not a sulfur source.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- The biosynthesis of essential sulfur-containing compounds involves carbon-sulfur bond formation, a process not fully understood.
- Radical-S-adenosylmethionine (radical-SAM) enzymes, like MiaB and RimO, are implicated in sulfur insertion into biomolecules.
- These enzymes possess two [4Fe-4S] clusters, with the role of the second cluster being a subject of debate.
Purpose of the Study:
- To elucidate the precise function of the second [4Fe-4S] cluster in radical-SAM enzymes MiaB and RimO.
- To investigate the mechanism of sulfur insertion catalyzed by these enzymes.
- To provide the first evidence for a novel sulfation mechanism involving these enzymes.
Main Methods:
- Enzymological assays to study enzyme activity and kinetics.
- Spectroscopic techniques to analyze the structure and function of the iron-sulfur clusters.
- Crystallographic studies to determine the high-resolution structures of MiaB and RimO.
Main Results:
- The second [4Fe-4S] cluster in MiaB and RimO does not act as a sacrificial sulfur source.
- Evidence supports a new sulfation mechanism where the second cluster is a true catalytic site.
- This cluster activates an exogenous sulfur cosubstrate at an exchangeable coordination site and remains intact during catalysis.
Conclusions:
- MiaB and RimO are true catalysts in sulfur insertion reactions.
- A novel mechanism for sulfur insertion involving activation of a sulfur cosubstrate at the second [4Fe-4S] cluster is proposed.
- This finding advances the understanding of radical-SAM enzyme mechanisms and sulfur biosynthesis.
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