Translocation of mRNA and tRNAs through the ribosome is catalyzed by a universally conserved elongation factor (EF-G in prokaryotes and EF-2 in eukaryotes). Previous studies have suggested that ribosome-bound EF-G undergoes significant structural rearrangements. Here, we follow the movement of domain IV of EF-G, which is critical for the catalysis of translocation, relative to protein S12 of the small ribosomal subunit using single-molecule FRET. We show that ribosome-bound EF-G adopts distinct conformations corresponding to the pre- and posttranslocation states of the ribosome. Our results suggest that, upon ribosomal translocation, domain IV of EF-G moves toward the A site of the small ribosomal subunit and facilitates the movement of peptidyl-tRNA from the A to the P site. We found no evidence of direct coupling between the observed movement of domain IV of EF-G and GTP hydrolysis. In addition, our results suggest that the pretranslocation conformation of the EF-G–ribosome complex is significantly less stable than the posttranslocation conformation. Hence, the structural rearrangement of EF-G makes a considerable energetic contribution to promoting tRNA translocation.

Previous structural studies suggested that ribosomal translocation is accompanied by large interdomain rearrangements of elongation factor G (EF-G). Here, we follow the movement of domain IV of EF-G relative to domain II of EF-G using ensemble and single-molecule Förster resonance energy transfer (smFRET). Our results indicate that ribosome-free EF-G predominantly adopts a compact conformation that can also, albeit infrequently, transition into a more extended conformation in which domain IV moves away from domain II. By contrast, ribosome-bound EF-G predominantly adopts an extended conformation regardless of whether it is interacting with pre- or posttranslocation ribosomes. Our data suggest that ribosome-bound EF-G may also occasionally sample at least one more compact conformation. GTP hydrolysis catalyzed by EF-G does not affect the relative stability of the observed conformations in ribosome-free and ribosome-bound EF-G. Our data support a model suggesting that, upon binding to a pretranslocation ribosome, EF-G moves from a compact to a more extended conformation. This transition is not coupled to, but likely precedes both GTP hydrolysis and mRNA/tRNA translocation.

Objective: The purpose of this retrospective study was to evaluate safety and efficacy end points of a postoperative antibiotic prophylaxis protocol in liver transplant (LT) patients, which was revised to limit antibiotic use. Methods: In the routine antibiotics group (RA), patients routinely received prophylactic antibiotics for around 3 days postoperatively for a variety of rationales, versus the limited antibiotics group (LA), in which patients received antibiotics for the treatment of secondary peritonitis. Patients were included if they were 18 or older and underwent liver transplant between January 2016 and September 2019. In total, 216 patients remained after exclusion: 118 patients in the RA group and 98 patients in the LA group. Results: We detected a significant difference in the primary end point of postoperative antibiotic days of therapy. The median days of therapy was 2 for the RA group and 0 for the LA group (P < 0.005). Significantly fewer patients received only intraoperative antibiotics in the RA group versus the LA group: 42 (35.6%) versus 76 (73.5%) respectively (P < .005). There was no significant difference in secondary or safety outcomes, including surgical site infections. Conclusions: This study provides evidence that limiting the duration of prophylactic antibiotics postoperatively and treating most patients with only intraoperative antibiotics is safe.

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