One polypeptide with two aminoacyl-tRNA synthetase activities

Area of Science:

• Molecular Biology
• Biochemistry
• Evolutionary Biology

Background:

• Certain archaea genomes lack dedicated cysteinyl-tRNA synthetases, enzymes crucial for protein synthesis.
• The synthesis of aminoacyl-tRNAs is fundamental for translating genetic information into proteins.

Purpose of the Study:

• To investigate the identity and function of the enzyme responsible for cysteinyl-tRNA synthesis in archaea lacking a canonical cysteinyl-tRNA synthetase.
• To explore the implications of an enzyme with dual aminoacyl-tRNA synthetase activity on substrate specificity and evolutionary origins.

Main Methods:

• Purification of the enzyme activity from Methanococcus jannaschii.
• Amino-terminal sequencing of the purified protein.
• Biochemical assays to determine substrate specificity.
• Genetic analysis to confirm enzyme function.

Main Results:

• A single enzyme with prolyl-tRNA synthetase identity was found to possess cysteinyl-tRNA synthetase activity.
• This archaeal prolyl-tRNA synthetase can aminoacylate both tRNA(Pro) and tRNA(Cys).
• The enzyme's dual function was confirmed through biochemical and genetic studies.

Conclusions:

• The findings challenge traditional concepts of enzyme substrate specificity in the context of protein synthesis.
• This dual-function enzyme provides potential insights into the evolutionary pathways of aminoacyl-tRNA synthetases.
• The study highlights the adaptability and diversity of molecular machinery in archaea.