Figure 1. AlphaFold model of the Atg2-Atg18 complex.― 254 ―Atg18 complex bridges SUVs and GUVs, facilitating lipid transfer from SUVs to GUVs through the central cavity of Atg2, thus supporting the bridge model of lipid transfer by the Atg2-Atg18 complex.In the Nur project, we first prepared purified protein of the full-length secreted form of Nur and measured its antimicrobial activity against E. coli. Contrary to previous reports, however, we did not detect any antimicrobial activity. Therefore, we divided Nur into multiple fragments, purified them individually, and evaluated their antimicrobial activities (minimum inhibitory concentration, MIC). We found that two fragments from the C-terminal region exhibited MIC values identical to ampicillin. Thus, it appeared that Nur acquires antimicrobial activity upon fragmentation. Next, we treated E. coli with fluorescently labeled Nur fragments and found that these fragments initially bound to the bacterial surface and subsequently translocated into the cells without disrupting the cell membrane. Similar results were observed in experiments using GUVs; Nur fragments bound to the membrane and translocated into the interior without compromising membrane integrity. Intriguingly, the Nur fragments formed liquid droplets within the bacterial cells, colocalizing with ribosomes. Fluorescence recovery after photobleaching (FRAP) experiments showed that Nur fragments displayed high mobility, while ribosomes in the same droplets exhibited significantly reduced mobility compared to their mobility in the absence of Nur fragments. Furthermore, we demonstrated that Nur fragments inhibited ribosomal translation activity. Taken together, these results indicate that Nur fragments represent a novel type of antimicrobial peptide that exerts antibacterial activity by altering ribosome dynamics, thereby inhibiting translation.PerspectivesThis study has significantly advanced our understanding of the lipid supply mechanism mediated by Atg2, a fundamental process underlying autophagy. Further elucidation of the complete autophagy mechanism is expected to establish a solid foundation for pharmaceutical applications. Additionally, our analysis of Nur
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