Menu
Institut de Biologie StructuraleGrenoble / France

Highlights

COVID19 : IBS info

Below is some information about IBS activities during this critical period. We will keep you informed on further developments on this webpage. Please stay safe !

New measures

Following the French Government measures to limit the spread of the Covid-19 and to protect IBS staff’ well-being, the IBS site is closed until further notice since March 16, 2020.
During this period, your contacts, whenever possible, are teleworking and may still be reached by email (to know more). Web conferencing software enables remote meetings.
In line with the IBS Continuity Plan, only a minimum number of staff members have to come on-site from time to time, to maintain activities considered indispensable for the safety of our installation.

Seminars & events

All scientific events until end of May are either cancelled or postponed (to know more).

Administrative info

Invoices are currently being processed by our finance team.

Internships

The internships due to start after 17 March have been cancelled, and according to the UGA indications, transformed into bibliographic internships.

Watching Measles virus factories at work in liquid droplets

Many viruses are known to form cellular compartments, also called viral factories. Paramyxoviruses, including measles virus, colocalize their proteomic and genomic material in puncta in infected cells. Researchers from FDP, VRM and IRPAS groups at IBS demonstrate that purified nucleo- (N) and phospho- (P) proteins of Measles virus form liquid-like membraneless organelles upon mixing in vitro. They identify weak interactions involving intrinsically disordered domains of N and P that are implicated in this process, one of which is essential for phase separation. Fluorescence allows them to follow the modulation of the dynamics of N and P upon droplet formation while NMR is used to investigate the thermodynamics of this process. RNA colocalizes to droplets, where it triggers assembly of N protomers into nucleocapsid-like particles that encapsidate the RNA. The rate of encapsidation within droplets is enhanced compared to the dilute phase, revealing one of the roles of liquid-liquid phase separation in Measles virus replication. This study allows us to observe viral factories in action for the first time. The presence of similar puncta in numerous negative sense RNA viruses suggests that the observations made here will be of general interest in the development of antiviral strategies.

Measles Virus Nucleo- and Phosphoproteins form Liquid-like Phase-Separated Compartments that Promote Nucleocapsid Assembly. Serafima Guseva Sigrid Milles, Malene Ringkjøbing Jensen, Nicola Salvi, Jean-Phillipe Kleman, Damien Maurin, Rob W.H. Ruigrok, Martin Blackledge. Science Advances ; Vol. 6, no. 14, eaaz7095

How an electron and a proton modulate protein binding to DNA

The bacterial protein RsrR that coordinates a [2Fe-2S] cluster, regulates the expression of genes involved either directly or indirectly in cell redox equilibrium. The redox state of this iron-sulfur cluster controls RsrR binding to its site in DNA ; only the +2 oxidized form binds to the nucleic acid. In 2019, the IBS/Metallo group in collaboration with Pr. Nick Le Brun (University of East Anglia, UK) published the crystal structure of RsrR (Volbeda et al., JACS 2019) that showed an unprecedented coordination of its iron-sulfur cluster by Cys, Cys, Glu and His. The comparison of the oxidized and reduced protein structures revealed two conformations for a conserved tryptophan residue (W), called Out (in green in the figure) and In (in orange), and the concomitant displacement of a histidine (H).
In this new study, both groups, in collaboration with Dr Jean-Marie Mouesca (CEA-DRF-IRIG-DIESE-SyMMES-CAMPE), have solved the crystal structure of an RsrR-DNA complex where the three key resides (W, H and Y in black in the figure) adopt a conformation closer to the Out form. By combining chemical modification of W, site-directed mutagenesis, X-ray crystallography, quantum calculations, molecular dynamics and metadynamics simulations, they have shown that Out and In correspond to the oxidized and reduced forms, respectively. In addition, they have determined that its reduction (1 in the figure) changes the pKa of the H histidine towards more basic values ; the resulting doubly-protonated H (2) leads to the significant displacement of W, H and Y (3) ; the dipole moment of W responds to electrostatic changes caused by the reduction. Finally, the In form, thus produced, dissociates from DNA (4).
This study paves the way for the understanding of the mechanism by which the RsrR protein regulates the universal NAD cofactor synthesis and function. This cofactor is involved in photosynthesis, ATP production and cell respiration.

Electron and Proton Transfers Modulate DNA Binding by the Transcription Regulator RsrR. Crack JC, Amara P, Volbeda A, Mouesca JM, Rohac R, Pellicer Martinez MT, Huang CY, Gigarel O, Rinaldi C, Le Brun NE, Fontecilla-Camps JC. J Am Chem Soc, 142(11):5104-5116 (2020).