Pre-transfer Editing of Serine Hydroxamate within the Active Site of Methanogenic-type Seryl-tRNA Synthetase

Abstract

Aminoacyl-tRNA synthetases (aaRSs) maintain fidelity of protein synthesis by matching only cognate amino acid-tRNA pairs. Aminoacylation occurs through activation of amino acid to yield aminoacyl-adenylate followed by transfer of acyl-moiety to tRNA. Error-prone aaRSs achieve high level of accuracy using inherent hydrolytic activities towards noncognate aminoacyl-adenylate or misacylated tRNA (pre- and post-transfer editing).Seryl-tRNA synthetases can be divided into two structurally different types: canonical and methanogenic-type. Both types have been shown to efficiently activate serine analogue serine hydroxamate (SerHX). Moreover, this analogue has been also eliminated by pre-transfer editing within the canonical synthetic site of yeast SerRS. Here we show that methanogenic-type SerRS from Methanosarcina barkeri clears misactivated SerHX similarly as the yeast enzyme: SerHX-adenylate is not expelled into solution, but is enzymatically hydrolyzed in a tRNA-independent manner. Since the enzyme lacks domain specialized in editing, this shows that methanogenic-type catalytic core is also capable to perform pre-transfer editing.