Electrostatic Potential in the tRNA Binding Evolution of Dihydrouridine Synthases

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Dihydrouridine (D) is a vital tRNA modification synthesized by dihydrouridine synthases (Dus).
• Dus enzymes typically have a catalytic domain (TBD) and a tRNA-binding helical domain (HD).
• Animal Dus2 uniquely possesses a double-stranded RNA binding domain (dsRBD) for tRNA recognition.

Purpose of the Study:

• Investigate the role of the helical domain (HD) in tRNA binding for animal Dus2.
• Understand the evolutionary divergence in tRNA binding mechanisms within the Dus enzyme family.

Main Methods:

• Homology modeling of yeast Dus2.
• Crystallographic analysis of a human Dus2 variant (TBD + HD).
• Site-directed mutagenesis to reintroduce specific residues into human Dus2.

Main Results:

• The helical domain (HD) of human Dus2 is less electropositive than yeast Dus2 due to specific residue substitutions (K/Q).
• Reintroducing positive charges (K304, K315) into human Dus2 restored functional tRNA binding.
• These electrostatic changes in HD are conserved in animal Dus2.

Conclusions:

• Electrostatic modifications in the HD of Dus2 enzymes are critical for establishing a distinct tRNA binding mode in animals.
• This highlights the role of domain evolution and charge modulation in enzyme function adaptation.