Direct FeS Cluster Involvement in Generation of a Radical in Lysine 2,3-Aminomutase

Lysine 2,3-aminomutase (KAM) belongs to a class of enzymes that use FeS clusters and S-adenosyl-l-methionine to initiate radical-dependent chemistry. Selenium K-edge X-ray absorption spectroscopic analysis of KAM poised at various stages of catalysis, in the presence of selenomethionine or Se-adenosyl-l-selenomethionine, reveals that the cofactor is cleaved only in the presence of dithionite and the substrate analogue trans-4,5-dehydrolysine. A new Fourier transform peak at 2.7 Å, assigned as a Se−Fe interaction, appears concomitant with this cleavage. This is the first demonstration of a direct interaction of S-adenosyl-l-methionine, or its cleavage products, with the FeS cluster in this class of enzymes.