O-Phosphoserine tRNA Selenocysteine tRNA Synthase (SEPSECS)

Autoantibodies to soluble liver antigen (SLA) and to liver and pancreas antigen (LP) occur in about 30% of all patients with autoimmune hepatitis.

The 21st amino acid, selenocysteine (sec), is distinct from other amino acids because it lacks its own tRNA synthetase and is the only amino acid synthesized on its cognate tRNA. Synthesis of sec begins with acylation of tRNA(sec) (TRSP) by seryl-tRNA synthetase (SARS) to give ser-tRNA(sec), which is subsequently phosphorylated by O-phosphoseryl-tRNA kinase (PSTK) to give O-phosphoseryl-tRNA(sec). SEPSECS catalyzes the final step of sec synthesis by converting O-phosphoseryl-tRNA(sec) to selenocysteinyl-tRNA(sec) using selenophosphate as the selenium donor.