Foscaldi, S. | Search bioRxiv

bioRxiv2021

Structural basis for the Pr-Pfr long-range signaling mechanism of a full-length bacterial phytochrome at the atomic level

Light sensing allows organisms to adapt to constantly changing environmental factors. Phytochromes constitute a widespread biological photoreceptor family that typically interconvert between two photostates called Pr (red light-absorbing) and Pfr (far-red light-absorbing). Despite the vast structural information reported on phytochromes, the lack of full-length structures at the (near-)atomic level in both pure Pr and Pfr states leaves gaps in the structural mechanisms involved in the signal transmission pathways during the photoconversion. Here we present three crystallographic structures from the plant pathogen Xanthomonas campestris virulence regulator bacteriophytochrome, including two full-length proteins, in the Pr and Pfr states. The structural findings, combined with mutational, biochemical and computational studies, allow us to describe the signaling mechanism of a full-length bacterial phytochrome at the atomic level, from the isomerization of the chromophore and the {beta}-sheet/-helix tongue transition to the remodeling of the quaternary assembly of the protein. TEASERCrystal structures of the full-length bacteriophytochrome XccBphP in both Pr and Pfr states unveil photoswitching mechanism

biophysics↗

bioRxiv2017

DDX3 is exploited by Arenaviruses to suppress type I interferons and favor their replication

Several arenaviruses cause hemorrhagic fever (HF) diseases that are associated with high morbidity and mortality in humans. Accordingly, HF arenaviruses have been listed as top-priority emerging diseases for which countermeasures are urgently needed. Because arenavirus nucleoprotein (NP) plays critical roles in both virus multiplication and immune-evasion, we used an unbiased proteomic approach to identify NP-interacting proteins in human cells. DDX3, a DEAD-box ATP-dependent-RNA-helicase, interacted with NP in both NP-transfected and virus-infected cells. Importantly, DDX3 deficiency compromised the propagation of both Old and New World arenaviruses, including the HF arenaviruses Lassa and Junin viruses. The DDX3 role in promoting arenavirus multiplication correlated with both a previously un-recognized DDX3 contribution to type I interferon suppression in arenavirus infected cells and a positive effect of DDX3 on viral RNA synthesis. Our results uncover novel mechanisms used by arenavirus to exploit the host machinery and subvert immunity, singling out DDX3 as a potential host target for developing new therapies against highly pathogenic arenaviruses.\n\nAUTHOR SUMMARYArenaviruses include severe clinical pathogens causing hemorrhagic fevers and have been recently incorporated by the World Health Organization in a list of critical emerging diseases for which additional research and identification of clinical targets is urgently required. A better understanding of how viral proteins interact with host cellular factors to favor arenavirus multiplication can illuminate novel pipelines on therapeutic strategies. Here we demonstrated that the ATP-dependent RNA helicase DDX3 interacted with the arenavirus nucleoprotein, which displays fundamental functions in different steps of the viral-cycle. Our work also revealed an unexpected new biology on the role that DDX3 might play during viral infections. In sharp contrast to previous studies showing DDX3 enhancement of IFN-I induction, we demonstrated that DDX3 suppressed IFN-I production at late time points after arenavirus infection, contributing to a DDX3 pro-viral effect. We also showed that early after infection, DDX3 pro-viral role was IFN-I independent and was mediated by DDX3 facilitation of viral RNA synthesis without affecting RNA translation. Altogether, our study established DDX3 as a critical host interacting partner of the arenavirus nucleoprotein and demonstrated two previously unrecognized DDX3-dependent strategies by which these deadly viruses exploit the host cellular machinery and suppress immunity.

microbiology↗