Mammalian HEMK1 Methylates Glutamine Residue of the GGQ Motif of Mitochondrial Release Factors

Despite limited reports on glutamine methylation, methylated glutamine is found to be highly conserved in a "GGQ" motif in both prokaryotes and eukaryotes. In bacteria, glutamine methylation of peptide chain release factors 1/2 (RF1/2) by the enzyme PrmC is essential for translational termination and transcript recycling. Two PrmC homologs, HEMK1 and HEMK2, are found in mammals. In contrast to those of HEMK2, the biochemical properties and biological significance of HEMK1 remain largely unknown. In this study, we demonstrated that HEMK1 is an active methyltransferase for the glutamine residue of the GGQ motif of all four putative mitochondrial release factors (mtRFs)—MTRF1, MTRF1L, MRPL58, and MTRFR. In HEMK1-deficient HeLa cells, GGQ motif glutamine methylation was absent in all the mtRFs. We examined cell growth and mitochondrial properties, but disruption of the HEMK1 gene had no considerable impact on the overall cell growth, mtDNA copy number, and mitochondrial membrane potential. Furthermore, mitochondrial protein synthesis was not affected in HEMK1 KO cells. Our results suggest that HEMK1 mediates the GGQ methylation of all four mtRFs in human cells; however, this specific modification seems mostly dispensable in cell growth and mitochondrial protein homeostasis under standard culture conditions.

QM calculations predict the energetics and infrared spectra of transient glutamine isomers in LOV photoreceptors

The isomerisation of a conserved glutamine residue along the early photocycle of 3 LOV domains is explored by QM calculations, revealing IR spectral shifts upon rotation in agreement with time-resolved experiments.

Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences

The conformational preferences of a series of short, aromatic-capped, glutamine-containing peptides have been studied under jet-cooled conditions in the gas phase.

A single amino acid change, Q114R, in the cleavage-site sequence of Newcastle disease virus fusion protein attenuates viral replication and pathogenicity

A key determinant of Newcastle disease virus (NDV) virulence is the amino acid sequence at the fusion (F) protein cleavage site. The NDV F protein is synthesized as an inactive precursor, F0, and is activated by proteolytic cleavage between amino acids 116 and 117 to produce two disulfide-linked subunits, F1 and F2. The consensus sequence of the F protein cleavage site of virulent [112(R/K)-R-Q-(R/K)-R↓F-I118] and avirulent [112(G/E)-(K/R)-Q-(G/E)-R↓L-I118] strains contains a conserved glutamine residue at position 114. Recently, some NDV strains from Africa and Madagascar were isolated from healthy birds and have been reported to contain five basic residues (R-R-R-K-R↓F-I/V or R-R-R-R-R↓F-I/V) at the F protein cleavage site. In this study, we have evaluated the role of this conserved glutamine residue in the replication and pathogenicity of NDV by using the moderately pathogenic Beaudette C strain and by making Q114R, K115R and I118V mutants of the F protein in this strain. Our results showed that changing the glutamine to a basic arginine residue reduced viral replication and attenuated the pathogenicity of the virus in chickens. The pathogenicity was further reduced when the isoleucine at position 118 was substituted for valine.