Crystal structure analysis reveals functional flexibility in the selenocysteine-specific tRNA from mouse

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Selenocysteine tRNAs (tRNA(Sec)) possess unique identity elements crucial for selenocysteine biosynthesis and protein decoding.
• The precise mechanisms by which these identity elements are recognized by interacting proteins remain incompletely understood.

Purpose of the Study:

• To elucidate the structural basis of tRNA(Sec) function through high-resolution crystallography.
• To investigate the roles of water molecules, metal ions, and specific modifications in tRNA(Sec) conformation and protein interactions.

Main Methods:

• Rational mutagenesis was employed to generate well-diffracting crystals of murine tRNA(Sec).
• X-ray crystallography was used to determine the structure of a truncated tRNA(Sec) ((ΔGCCA)RNA(Sec)) at 2.0 Å resolution.
• Structural comparisons, molecular modeling, and metal ion soaking experiments were conducted.

Main Results:

• The 2.0 Å crystal structure of (ΔGCCA)RNA(Sec) reveals global similarity to human tRNA(Sec) but highlights flexible regions involved in induced fit binding.
• Water molecules stabilize alternative conformations of the anticodon stem-loop, and a U34 modification favors a ribosome-functional conformation.
• Eight potential divalent metal ion binding sites were identified, though bound ions did not significantly stabilize specific structural features.

Conclusions:

• This study provides the highest resolution structure of tRNA(Sec) to date, offering critical insights into its conformational flexibility.
• The findings suggest that conformational dynamics, influenced by water and modifications, are key to tRNA(Sec) interactions with biosynthetic and decoding machinery.