REGULATION OF HUMAN CYTIDINE TRIPHOSPHATE SYNTHETASE 2 BY PHOSPHORYLATION

Abstract

Cytidine triphosphate synthetase (CTPS) is the rate‐limiting enzyme that catalyzes the de novo synthesis of CTP from UTP although little is known about the regulatory mechanisms that control the activity of this enzyme. In addition to UTP, CTPS requires the substrates ATP, GTP, and glutamine. Previous studies determined that an increase in phosphorylation of the carboxyl‐terminal regulatory domain (CRD) decreased CTPS1 activity. Therefore, the purpose of this study was to identify the major phosphorylation sites in the CRD of human CTPS2 and to determine their influence on CTPS2 activity. Using mass spectrometry, five potential phosphorylation sites were indentified: S564, Y567, S568, S571, and S574. After mutation of each of these sites, kinetic analysis of both wild‐type and mutated CTPS2 were performed. Analysis of a Ser/Ala mutation at S568 (S568A CTPS2), at various glutamine concentrations, showed much higher enzymatic activity compared to wild type CTPS2 (WT‐CTPS2). In comparison, mutation of the other phosphorylation sites had minimal effects on CTPS2 activity. In conclusion, this study investigated the effects of phosphorylation on CTPS2 activity and identified S568 as a major phosphorylation site in CTPS2.