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FOR THE RECORD

Structural studies of the interaction of S-adenosylmethionine with the [4Fe-4S] clusters in biotin synthase and pyruvate formate-lyase activating enzyme

¹ Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA
² Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA

Reprint requests to: Robert A. Scott, Department of Chemistry, University of Georgia, Athens, GA 30602-2556, USA; e-mail: scott{at}chem.uga.edu; fax: (706) 542-9454.

The diverse reactions catalyzed by the radical-SAM superfamily of enzymes are thought to proceed via a set of common mechanistic steps, key among which is the reductive cleavage of S-adenosyl-L-methionine (SAM) by a reduced [4Fe-4S] cluster to generate an intermediate deoxyadenosyl radical. A number of spectroscopic studies have provided evidence that SAM interacts directly with the [4Fe-4S] clusters in several of the radical-SAM enzymes; however, the molecular mechanism for the reductive cleavage has yet to be elucidated. Selenium X-ray absorption spectroscopy (Se-XAS) was used previously to provide evidence for a close interaction between the Se atom of selenomethionine (a cleavage product of Se-SAM) and an Fe atom of the [4Fe-4S] cluster of lysine-2,3-aminomutase (KAM). Here, we utilize the same approach to investigate the possibility of a similar interaction in pyruvate formate-lyase activating enzyme (PFL-AE) and biotin synthase (BioB), two additional members of the radical-SAM superfamily. The results show that the latter two enzymes do not exhibit the same Fe-Se interaction as was observed in KAM, indicating that the methionine product of reductive cleavage of SAM does not occupy a well-defined site close to the cluster in PFL-AE and BioB. These results are interpreted in terms of the differences among these enzymes in their use of SAM as either a cofactor or a substrate.

Keywords: Biotin synthase (BioB); iron-sulfur cluster; pyruvate formate-lyase activating enzyme (PFL-AE); radical SAM superfamily; X-ray absorption fine structure; X-ray absorption spectroscopy

Abbreviations: SAM, S-adenosyl-L-methionine • Se-XAS, selenium X-ray absorption spectroscopy • KAM, lysine-2,3-aminomutase • PFL-AE, pyruvate formate-lyase activating enzyme • BioB, biotin synthase • Fe-S, iron-sulfur • PFL, pyruvate formate-lyase • ANAR, anaerobic ribonucleotide reductase • LipA, lipoate synthase • DTB, dethiobiotin • ENDOR, electron-nuclear double resonance • SeMet, selenomethionine • Se-SAM, Se-adenosyl-L-selenomethionine

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