セリンパルミトイル転移酵素における基質アナログを用いたキノノイド中間体形成過程の解析

抄録

Serine palmitoyltransferase (SPT) is a key enzyme of sphingolipid biosynthesis and catalyzes the pyridoxal 5'-phosphate (PLP)-dependent decarboxylative condensation reaction of L-serine with palmitoyl-CoA to generate 3-ketodihydrosphingosine. The binding of L-serine alone to SPT leads to the formation of the external aldimine. The further addition of a non-reactive palmitoyl-CoA analogue caused the apparent accumulation of the quinonoid. NMR studies showed that the hydrogen-deuterium exchange of the α-proton of L-serine was 100-fold accelerated by the binding of the palmitoyl-CoA analogue, showing a remarkable substrate synergism in SPT. Structural model simulations on SPT suggest that the binding of palmitoyl-CoA to SPT induced a conformational change in the PLP-L-serine external aldimine, and that the alternative interactions of His 159 with the two substrates plays an important role in it. This is the unique mechanism of SPT that prevents the formation of the reactive intermediate before the binding of the second substrate.