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Structural studies of the interaction of S ‐adenosylmethionine with the [4Fe‐4S] clusters in biotin synthase and pyruvate formate‐lyase activating enzyme
Author(s) -
Cosper Michele M.,
Cosper Nathaniel J.,
Hong Wei,
Shokes Jacob E.,
Broderick William E.,
Broderick Joan B.,
Johnson Michael K.,
Scott Robert A.
Publication year - 2003
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.0302203
Subject(s) - chemistry , stereochemistry , enzyme , formate , cleavage (geology) , lyase , cofactor , iron–sulfur cluster , active site , biochemistry , catalysis , biology , fracture (geology) , paleontology
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.