AKIN10, a representative Arabidopsis SNF1-related protein kinase 1 (Sn RK1), phosphorylates and downregulates plant HMG-CoA reductase.

HMG-CoA reductase ( HMGR) is a key enzyme in the mevalonate pathway for sterols and cytosolic isoprenoid production. Although HMGR kinases from spinach, barley, and cauliflower tissues have been strongly suggested as members of SNF1-related protein kinases 1 (Sn RK1), the phosphorylation and inactivation of HMGR by plant Sn RK1s has not been demonstrated. In this study, we elucidated that AKIN10, an Arabidopsis Sn RK1, acts as an HMGR kinase. The recombinant AKIN10 phosphorylates and inactivates At HMGR1S using recombinant GRIK1 as the AKIN10 activator. In contrast, AKIN10- GRIK1 fails to inactivate At HMGR1S-S577A, suggesting that this is achieved through Ser577 phosphorylation. Moreover, phosphorylation is detected not only in At HMGR1S but also in At HMGR1S-S577A, suggesting the presence of a novel regulatory mechanism of plant HMGR. [ABSTRACT FROM AUTHOR]