The seminar will take place, the 8th of June 2017, at 4 pm, at the ENSCBP amphitheater, Building B, allée Geoffroy Saint-Hilaire, Pessac.
Professor Christian Salesse
Département d’ophtalmologie, PROTEO, Université Laval and CUO-Recherche, Centre de recherche du CHU de Québec, Québec (QC) Canada
Light absorption by the chromophore (11-cis-retinal) of the visual pigment of rod photoreceptors (rhodopsin) results in its isomerization to all-trans-retinal. All-trans-retinal is then conveyed to the retinal pigment epithelium where it is recycled to 11-cis-retinal through the « retinoids visual cycle ». One of the key enzymes of the visual cycle is lecithin retinol acyltransferase (LRAT). LRAT is a membrane-associated protein. We have thus expressed a truncated LRAT (tLRAT, amino acids 31-196) without its N- and C-terminal α-helices. The enzymatic reaction catalyzed by LRAT is postulated to take place in two steps. 1) Non-acylated LRAT first hydrolyzes the sn-1 fatty acyl chain of phospholipids, which results in the production of acylated LRAT. 2) Acylated LRAT then transfers its acyl chain to retinol, which produces a retinyl ester. We have recently developed the first reliable method to characterize its biochemical properties in details. Then, the uniformly 15N,13C-labeled C161S/C168S-tLRAT sample allowed us to assign 100% of backbone amides and 100% of the 13C’, 13Cα and 13Cβ by Nuclear Magnetic Resonance (NMR). We derived the secondary structure of tLRAT based on the assigned chemical shifts. Moreover, several mutations of LRAT (Y61A-, A106T-, R109L-, P173L- and S175R) are leading to a complete loss of vision. These mutants have very little or no enzymatic activity. The comparison between our 15N-Heteronuclear Single Quantum Coherence (HSQC) NMR spectra of tLRAT and those of the P173L-, Y61A-, A106T- and S175R-tLRAT mutants allowed to suggest that these mutations result in local structural changes in the protein. The N- and C-terminal segments of LRAT have also been studied to determine their respective contribution to the membrane anchoring of LRAT. Furthermore, our membrane binding experiments with tLRAT suggested that it has a strong affinity for membranes despite the absence of its N- and C-terminal hydrophobic segments. Other regions of LRAT must be involved in its membrane anchoring such as an α-helical internal segment that we have identified from our NMR characterization.
Christian Salesse graduated in biophysics from the Université du Québec à Tois-Rivières (UQTR). He was then a postdoctoral fellow at Mainz Universität in Germany. He then became professor at the UQTR for 14 years until he moved to Université Laval in 2002. He has been a FRQS fellow from the Junior 1 to the National level. He is also adjunct professor at Jilin University in China. He was an invited professor at several universities in France and Portugal. He is the head of the Vision research unit at the Centre de recherche du CHU de Quebec and of the retina division of the FRQS Vision research network. He organized several provincial and international meetings.