Structure and mechanism of the glycyl radical enzyme pyruvate formate-lyase[6]

The enzyme pyruvate formate-lyase (PFL) catalyzes the reversible conversion of pyruvate and CoA into acetyl-CoA and formate, which has a central role in anaerobic glucose fermentation by E. coli cells and other bacteria [1]. PFL a 2 × 85 kDa homodimer is the first example of a radical enzyme where the spin was found to be located on the polypeptide backbone Cα-atom of a glycyl residue (Gly 734) [2,3]. Biochemical studies revealed that the substrate conversion by PFL proceeds via a homolytic mechanism and occurs through two half-reactions involving an acetyl-enzyme intermediate ( E + pyruvate acetyl-E + formate; acetyl-E + CoA E + acetyl-CoA) [4]. In the active site two adjacent cysteinyl residues (Cys 418, Cys 419) play a central role in carrying the intermediary acetyl. Moreover, it has been proposed that a thiyl radical from one of these two cysteine residues would be generated by the glycyl radical and used to promote the homolytic substrate cleavage.