Catalyzes the interconversion of L-alpha-lysine and L-beta-lysine. Is involved in the biosynthesis pathway of N6-acetyl-beta-lysine, a compatible solute produced by methanogenic archaea that helps cells to cope with salt stress (Probable). L-lysine = (3S)-3,6-diaminohexanoate Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Binds 1 zinc ion per subunit. Transcription is induced at high salt concentrations. Forms part of an operon with ablB. Belongs to the radical SAM superfamily. KamA family.