IECB
Seminars
Monday, December 5
14:00 am
@ IECB auditorium
Dr. Sébastien GOEB
Laboratory MOLTECH-Anjou, Angers University
Stimuli responsive coordination cages
Coordination driven self-assembly has allowed the preparation of many molecular polygons and polyhedrons with remarkable properties. They are obtained by association of polytopic ligands and complexes showing a pre-organized geometry. The corresponding host cavities offer promising opportunities for applications in molecular recognition or even in guest transport. We focused our attention for several years in the design of electro-active self-assembled 2D and 3D discrete structures based on the tetrathiafulvalene unit (TTF) and derivatives (exTTF and DTF for example) with the aim of controlling the guest release thanks to an electrochemical stimulus. We are also interested in understanding the key parameters governing the formation of an emergent class of coordination assemblies, i.e. interlocked cages. We believe that such compact objects could offer promising opportunities in controlling the structural organization of donor and acceptor units. For example, we demonstrated recently that truxene based ligands, associated with dinuclear Ruthenium or Rhodium complexes, can produce this type of compact interlocked systems.
Host: Yann FERRAND
Thursday, December 8
11:15 am
@ IECB auditorium
Dr. Ana S. Ramirez
Institute of Molecular Biology and Biophysics, ETH Zurich
Structural and mechanistic insight into protein N-glycosylation
Protein N-glycosylation is a post-translational modification that exists in all domains of life. It consists of two main steps: (1) biosynthesis of a lipid-linked oligosaccharide (LLO), and (2) the glycan transfer from LLO to asparagine residues of acceptor proteins, a process catalyzed by oligosaccharyltransferase (OST) enzymes. N-glycosylation plays essential roles in several cellular processes, such as protein folding, function, and cell-cell communication. During the last years, my research has focused on the structural and mechanistic investigation of N-glycosylation enzymes in bacteria, humans, yeast, and protozoan parasites using a multidisciplinary approach that involves protein biochemistry, chemo-enzymatic glycan elongation, X-ray crystallography, and single-particle Cryo-EM. We described a counting mechanism for PglH, a processive glycosyltransferase involved in LLO biosynthesis in the bacterial human pathogen Campylobacter jejuni [1]. In higher eukaryotes, where OST enzymes are multimeric membrane complexes located at the membrane of the endoplasmic reticulum (ER), we determined cryo-EM structures of the two OST enzymes that co-exist in human cells, revealing the molecular basis of their specific function in catalyzing co-translational or post-translational N-glycosylation [2]. Recently, we elucidated cryo-EM structures of the yeast multimeric OST complex in different functional states revealing the molecular basis of substrate recognition and catalysis [3].
1. Ramírez, A. S. et al. Structural basis of the molecular ruler mechanism of a bacterial glycosyltransferase. Nat. Commun. 9, 445 (2018).
2. Ramírez, A. S., Kowal, J. & Locher, K. P. Cryo-electron microscopy structures of human oligosaccharyltransferase complexes OST-A and OST-B. Science 366, 1372–1375 (2019).
3. Ramírez A.S., de Capitani M, Pesciullesi G, Kowal J, Bloch JS, Irobalieva RN, Reymond J-L, Aebi M, Locher KP.. Structural basis of glycan recognition and reaction priming in eukaryotic oligosaccharyltransferase (in revision).
Host: Nicolas REYES