Arabidopsis nicotianamine synthases comprise a common core-NAS domain fused to a variable autoinhibitory C terminus.

Nicotianamine synthase (NAS) catalyzes the biosynthesis of the low-molecular-mass metal chelator nicotianamine (NA) from the 2-aminobutyrate moieties of three SAM molecules. NA has central roles in metal nutrition and metal homeostasis of flowering plants. The enzymatic function of NAS remains poorly understood.