Human translation initiation factor eIF4G1 possesses a low-affinity ATP binding site facing the ATP-binding cleft of eIF4A in the eIF4G/eIF4A complex

Auxiliary ATP binding sites support DNA unwinding by RecBCD

The RecBCD helicase initiates double-stranded break repair in bacteria by processively unwinding DNA with a rate approaching ∼1,600 bp·s⁻¹, but the mechanism enabling such a fast rate is unknown. Employing a wide range of methodologies — including equilibrium and time-resolved binding experiments, ensemble and single-molecule unwinding assays, and crosslinking followed by mass spectrometry — we reveal the existence of auxiliary binding sites in the RecC subunit, where ATP binds with lower affinity and distinct chemical interactions as compared to the known catalytic sites. The essentiality and functionality of these sites are demonstrated by their impact on the survival of E.coli after exposure to damage-inducing radiation. We propose a model by which RecBCD achieves its optimized unwinding rate, even when ATP is scarce, by using the auxiliary binding sites to increase the flux of ATP to its catalytic sites.

RecBCD is a remarkably fast DNA helicase. Using a battery of biophysical methods, Zananiri et. al reveal additional, non-catalytic ATP binding sites that increase the ATP flux to the catalytic sites that allows fast unwinding when ATP is scarce.

EIF4G1 is a novel candidate gene associated with severe asthenozoospermia

BACKGROUND

Asthenozoospermia (AZS), also known as asthenospermia, is characterized by reduced motility of ejaculated spermatozoa and is detected in more than 40% of infertile patients. Because the proportion of progressive spermatozoa in severe AZS is <1%, severe AZS is an urgent challenge in reproductive medicine. Several genes have been reported to be relevant to severe asthenospermia. However, these gene mutations are found only in sporadic cases and can explain only a small fraction of severe AZS, so additional genetic pathogenies need to be explored.

METHODS AND RESULTS

By screening the variant genes in a patient with severe AZS using whole exome sequencing, we identified biallelic mutations c.2521C>T: p.(Pro841Ser) (NC_000003.11: g.184043412C>T) in exon13 and c.2957C>G: p.(Ala986Gly) (NC_000003.11: g.184045117C>G) in exon17 in the eukaryotic translation initiation factor 4 gamma 1 gene (EIF4G1, RefSeq: NM_004953.4, OMIM: 600495) of the patient. Both of the mutation sites are rare and potentially deleterious. Transmission electron microscopy analysis showed a disrupted axonemal structure with mitochondrial sheath defects. The EIF4G1 protein level was extremely low, and the mitochondrial marker cytochrome c oxidase subunit 4I1 (COXIV, OMIM: 123864) and mitochondrially encoded ATP synthase 6 (ATP6, OMIM: 516060) protein levels were also decreased in the patient's spermatozoa as revealed by WB and IF analysis. This infertility associated with this condition was overcome by intracytoplasmic sperm injections, as his wife became pregnant successfully.

CONCLUSION

Our experimental findings indicate that the EIF4G1 gene is a novel candidate gene that may be relevant to severe AZS.