title: Structural studies of the interaction of S-adenosylmethionine with the [4Fe-4S] clusters in biotin synthase and pyruvate formate-lyase activating enzyme.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, GA 30602-2556, USA.
authors.forename: Michele M
authors.initials: MM
authors.lastname: Cosper
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Cosper
authors.forename: Wei
authors.initials: W
authors.lastname: Hong
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Shokes
authors.forename: William E
authors.initials: WE
authors.lastname: Broderick
authors.forename: Joan B
authors.initials: JB
authors.lastname: Broderick
authors.forename: Michael K
authors.initials: MK
authors.lastname: Johnson
authors.forename: Robert A
authors.initials: RA
authors.lastname: Scott
mesh_terms: D000123:Acetyltransferases; D000426:Alcohol Dehydrogenase; D000445:Aldehyde Oxidoreductases; D003067:Coenzymes / Q000737:chemistry; D004789:Enzyme Activation; D004798:Enzymes / Q000737:chemistry*; D029968:Escherichia coli Proteins; D007501:Iron / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008715:Methionine / Q000737:chemistry; D009097:Multienzyme Complexes; D012436:S-Adenosylmethionine / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D013057:Spectrum Analysis; D013379:Substrate Specificity; D013466:Sulfurtransferases / Q000737:chemistry*
chemical_list: D003067:Coenzymes; D004798:Enzymes; D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; D009097:Multienzyme Complexes; D012436:S-Adenosylmethionine; D008715:Methionine; D007501:Iron; D000426:Alcohol Dehydrogenase; C068383:adhE protein, E coli; D000445:Aldehyde Oxidoreductases; D000123:Acetyltransferases; C040285:pyruvate formate-lyase activating enzyme; D013466:Sulfurtransferases; C057985:biotin synthetase; D008239:Lysine