glycyl-[protein] + reduced [flavodoxin] + S-adenosyl-L-methionine = 5'-deoxyadenosine + glycin-2-yl radical-[protein] + H(+) + L-methionine + semiquinone [flavodoxin] Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Belongs to the organic radical-activating enzymes family.