Crystal Structure of the 14-3-3ζ:Serotonin N-Acetyltransferase Complex: A Role for Scaffolding in Enzyme Regulation

Serotonin N-acetyltransferase (AANAT) controls the daily rhythm in melatonin synthesis. When isolated from tissue, AANAT copurifies with isoforms ϵ and ζ of 14-3-3. We have determined the structure of AANAT bound to 14-3-3ζ, an association that is phosphorylation dependent. AANAT is bound in the central channel of the 14-3-3ζ dimer, and is held in place by extensive interactions both with the amphipathic phosphopeptide binding groove of 14-3-3ζ and with other parts of the central channel. Thermodynamic and activity measurements, together with crystallographic analysis, indicate that binding of AANAT by 14-3-3ζ modulates AANATʹs activity and affinity for its substrates by stabilizing a region of AANAT involved in substrate binding.