Oligomerization and a distinct tRNA-binding loop are important regulators of human arginyl-transferase function

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Arginyl-transferase (ATE1) is a crucial enzyme in protein modification, attaching arginine to substrates.
• ATE1 deficiency in mice causes severe developmental defects, including cardiovascular and neurological issues, leading to embryonic lethality.
• While yeast ATE1 mechanisms are known, the structure-function relationship in higher organisms remains unclear.

Purpose of the Study:

• To elucidate the three-dimensional structure of human arginyl-transferase (ATE1).
• To investigate the structural basis of human ATE1's interaction with its tRNA cofactor and peptide substrate.
• To understand the structure-function relationship of human ATE1 in higher eukaryotes.

Main Methods:

• X-ray crystallography was used to determine the structure of human ATE1 in apo-state and complex with tRNA and peptide.
• Biochemical assays were performed to assess the enzymatic activity of ATE1 mutants.
• Cellular localization and substrate accumulation studies were conducted.

Main Results:

• Human ATE1 forms a symmetric homodimer in the apo-state, which dissociates upon substrate binding, unlike its yeast counterpart.
• A unique, extended loop in human ATE1 interacts extensively with the T-arm of tRNA^Arg.
• Mutations in key substrate-binding residues abolish ATE1 enzymatic activity and lead to substrate accumulation in cells.

Conclusions:

• The dimeric structure and substrate-induced dissociation of human ATE1 are critical for its function.
• The unique loop and tRNA interactions highlight species-specific adaptations in ATE1 structure and function.
• Understanding human ATE1 structure provides insights into its role in cellular processes and potential therapeutic targets.