14 Modification of glutamine residues in proteins involved in translation

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Protein glutamine methylation is a rare modification, primarily observed on proteins involved in ribosomal functions.
• This modification occurs as a mono-methylation on the side-chain amide nitrogen (N5) of glutamine residues.

Purpose of the Study:

• To investigate the role of glutamine methylation in polypeptide release factor (RF) function and its impact on translation termination.
• To explore the significance of glutamine methylation on ribosomal protein L3 in bacterial ribosome assembly.

Main Methods:

• Analysis of the effects of RF methylation defects on translation fidelity and cell growth.
• Characterization of the glutamine methyltransferases (MTase) and their catalytic mechanisms, including the [D/N]PPY motif.

Main Results:

• Defects in RF methylation lead to significant growth defects and increased read-through of stop codons.
• Ribosomal protein L3 methylation, found only in bacteria, is not essential but may aid ribosome assembly.
• Gin methyltransferases utilize a conserved [D/N]PPY motif for catalysis on neutral planar amidesubstrates, extending beyond DNA N-MTases.

Conclusions:

• Glutamine methylation plays a critical role in accurate polypeptide chain termination via RF modification.
• Bacterial ribosomal protein L3 methylation contributes to efficient ribosome structure formation.
• The [D/N]PPY motif in Gin methyltransferases has broader substrate specificity than previously understood.