ILL Chadwick Amphitheatre
The high resolution structures of the 30S subunit and more recently the entire ribosome have shed light on how the ribosome ensures the fidelity of translation. We will describe our studies on the nature of the recognition of codon-anticodon base pairing by the 30S ribosomal subunit, and how this leads to a series of conformational changes that results in the hydrolysis of GTP by elongation factor Tu, leading to the acceptance of the new amino acyl tRNA for the formation of a peptide bond.
Hosted by Jo Zaccai (ILL)
room 337, Central Building
PARTICIPANTS WHO HAVE NO BADGES ALLOWING ENTRANCE TO THE ILL-ESRF SITE ARE REQUESTED TO CONTACT Isabelle Combe tel +33 (0)438 88-19-92.
hosted by S. McSweeney
IBS seminar room
room 337, ESRF Central Building
PARTICIPANTS WHO HAVE NO BADGES ALLOWING ENTRANCE TO THE ILL-ESRF SITE ARE REQUESTED TO CONTACT Claudine Romero tel +33 (0)476 88-20-27.
Hosted by Sean McSweeney
IBS seminar room
TLR4 and MD-2 form a heterodimer that recognizes LPS from Gram negative bacteria. Eritoran is a candidate anti-sepsis drug that antagonizes LPS activity by binding to the TLR4-MD-2 complex. We determined the crystal structures of TLR4-MD-2 in complex with Eritoran and LPS. TLR4 is an atypical member of the LRR family and is composed of N-terminal, central and C-terminal domains. The b sheet of the central domain shows unusually small radii and large twist angles. MD-2 binds to the concave surface of the N-terminal and central domains. Agonistic LPS induced the formation of an “m”-shaped receptor multimer composed of two copies of the TLR4-MD-2-LPS complex arranged in a symmetrical fashion. LPS interacts with a large hydrophobic pocket in MD-2 and directly bridges the two components of the multimer. Five of the six lipid chains of LPS are buried deep inside the pocket and the remaining chain is exposed to the surface of MD-2, forming a hydrophobic interaction with the conserved phenylalanines of TLR4. The F126 loop of MD-2 undergoes localized structural change and supports this core hydrophobic interface by making hydrophilic interactions with TLR4. Eritoran binds to the LPS pocket in MD-2 and blocks LPS binding and TLR4-MD-2 heterotetramerization. Structural comparison of the TLR4-MD-2-LPS complex with the TLR4-MD-2-Eritoran complex indicates that two additional lipid chains in LPS displace the phosphorylated glucosamine backbone towards the solvent area by 5 angstrom. This structural shift allows phosphate groups of LPS to contribute to receptor multimerization by forming ionic interactions with a cluster of positively charged residues in TLR4 and MD-2. The TLR4-MD-2-LPS structure illustrates the remarkable versatility of the ligand recognition mechanisms employed by the TLR family, which is essential for defense against diverse microbial infection. We propose that formation of the TLR dimer brings the intracellular TIR domains close to each other to promote dimerization and initiate signaling.
Host: C. Petosa
IBS seminar Room
As formalized by Maynard-Smith, major evolutionary transitions of function and structure must occur gradually, and smoothly, through functional intermediates states. However, the nature of such transitions and intermediates remains largely unknown. To explore this process, we have used laboratory evolution to generate a complete trajectory: starting from a promiscuous aryl esterase activity (kcat/KM = 1.4×102), 105 fold less efficient than the native activity of a phosphotriesterase, incremental sequence changes gradually produced a smooth ‘functional switch’, involving a 4×108-fold reversal in the relative catalytic efficiencies, generating an efficient aryl esterase (kcat/KM = 5 x 106). Structural analysis has been used to investigate the structure-function relationship, revealing the ‘smoothness’ of the transition is based upon the ability of the protein to adopt a range of conformations with different catalytic properties. In this sense, evolution of new function can be viewed as a gradual shift in the conformational equilibrium of an enzyme, rather than a series of discrete changes. Axe
Where: Institut Jean Roget, Salle de Conférence (5th Floor),
Faculté de Médecine-Pharmacie, Domaine de la Merci, La Tronche.
Contact: Cordelia.Bisanz@ujf-grenoble.fr, Tel : 04 76 63 74 74
ILL Chadwick Amphitheatre
hosted by Celeste Sele (UVHCI)
IBS seminar room
Archaea, prokaryotes representing the third domain of life, often thrive under conditions approaching the physical limits of life (high temperature and salinity), which continuously attack the integrity of the genetic material. To understand how these fascinating organisms efficiently duplicate and repair their chromosomes under extreme conditions, we have been working on the identification and characterization of protein complexes required for genome maintenance in hyperthermophilic and halophilic archaea. This presentation will summarize how our work has led to the discovery of a novel family of DNA metabolic enzymes and DNA repair endonucleases. Special attention will be given to the structural (crystallography, SAXS) and functional characterization of these previously uncharacterized enzymes. Moreover, in a second part of my talk, I will discuss how our work has led to the unexpected discovery of a new drug target and provided the structural basis for rational design of anti-microbial compounds
host: Bruno Franzetti (IBS)
IBS seminar room
HDR defence: The short is: “a lot”. It was transient absorption spectroscopy on geminate recombination in myoglobin that led Hans Frauenfelder to constructing his picture of protein’s hierarchical energy landscape. And even before that (in 1973), Joseph Lakowicz and Gregorio Weber at UIUC used quenching of tryptophan fluorescence by oxygen diffusing to solvent-inaccessible protein regions to conclude that “proteins, in general, undergo rapid structural fluctuations on the nanosecond time scale “ . The not-so-short answer is that the present HDR thesis is written at a point where, after a decade of applying transient absorption spectroscopy to understand light induced electron transfer in a variety of enzymes, I am about to change the angle of attack and ask how these techniques and enzymes could be of help to solve some problems that are addressed in the IBS environment, namely protein dynamics, both structural and functional. It is for this reason that the answer will have to be delayed to the third and final part, “future”, that deals with the perspectives. Meanwhile, the first part, “past”, is dedicated to showing on the example of the “paradigm” enzyme –DNA photolyase-, what transient absorption spectroscopy is capable of and the middle part, “present” dresses a very short review into the literature on protein dynamics. In the final section, I will delineate ways how optical spectroscopy could interact with projects existing or emerging in the protein dynamics community at IBS and thus contribute elements of an answer to the title question. Axe
IBS seminar room
IBS seminar room
