Identification of an Intrinsically Disordered Region\n(IDR) in Arginyltransferase 1 (ATE1)

Arginyltransferase 1 (ATE1) catalyzes\narginylation, an important\nposttranslational modification (PTM) in eukaryotes that plays a critical\nrole in cellular homeostasis. The disruption of ATE1 function is implicated\nin mammalian neurodegenerative disorders and cardiovascular maldevelopment,\nwhile posttranslational arginylation has also been linked to the activities\nof several important human viruses such as SARS-CoV-2 and HIV. Despite\nthe known significance of ATE1 in mammalian cellular function, past\nbiophysical studies of this enzyme have mainly focused on yeast ATE1,\nleaving the mechanism of arginylation in mammalian cells unclear.\nIn this study, we sought to structurally and biophysically characterize\nmouse (Mus musculus) ATE1. Using size-exclusion\nchromatography (SEC), small-angle X-ray scattering (SAXS), and hydrogen–deuterium\nexchange mass spectrometry (HDX-MS), assisted by AlphaFold modeling,\nwe found that mouse ATE1 is structurally more complex than yeast ATE1.\nImportantly, our data indicate the existence of an intrinsically disordered\nregion (IDR) in all mouse ATE1 splice variants. However, comparative\nHDX-MS analyses show that yeast ATE1 does not have such an IDR, consistent\nwith prior X-ray, cryo-EM, and SAXS analyses. Furthermore, bioinformatics\napproaches reveal that mammalian ATE1 sequences, as well those as\nin a large majority of other eukaryotes, contain an IDR-like sequence\npositioned in proximity to the ATE1 GNAT active-site fold. Computational\nanalysis suggests that the IDR facilitates the formation of a complex\nbetween ATE1 and tRNA<sup>Arg</sup>, adding a new complexity to the\nATE1 structure and providing new insights for future studies of ATE1\nfunctions.