30 juin 2017: Séminaire du Dr. P. GREIMEL -Japan     

Invité par le Dr. Hullin-Matsuda, (Equipe 4  CarMeN), le Dr. Peter GREIMEL (RIKEN-Brain Science Institute- Japon) a présenté un séminaire CarMeN sur le site de l’INSA le 30 juini en salle de réunion  de l’IMBL (15 avenue Jean Capelle, Villeurbanne)

Titre:  « Recent Progress Toward BMP Structure and Biosynthesis and the Dynamics of Sphingolipid-Toxin Interaction« 

Résumé:

The glycerophospholipid bis(monoacylglycerol)phosphate (BMP) is a minor constituent in mammalian cells, but is specifically enriched in internal membranes of digestive organelles, such as late endosomes (LE) and lysosomes (Lyso). The digestive organelles are the waste treatment and recycling center in the cells, separating the hydrolytic enzymes needed to digest endocytosed particles or cellular waste, including aged lipids, proteins and even whole organelles, from the remainder of the cell. In this acidic environment, BMP plays a vital role by providing the suitable environment for these hydrolytic enzymes to work and is involved in cholesterol egress. Perturbation of BMP metabolism strongly affects glycosphingolipid degradation, cholesterol homeostasis and may also be a relevant factor in atherosclerosis.

Probing the native acylation pattern of lysophospholipids is difficult due to the inherent ability of ester groups to migrate between adjacent hydroxyl functions. The regioisomer composition of native BMP has been the subject of some scientific discussion and Luquain et al demonstrated that TLC-purified BMP is primarily esterified on the primary hydroxyl function. To overcome possible ester migration during isolation, a simple LC-MS/MS based assay system capable to separate BMP based on its fatty acid composition as well as its regioisomer was developed and the native BMP regioisomer identified. Additionally, recent progress towards identifying enzymes involved in BMP biosynthesis will be discussed.

Lipid rafts, regions of the plasma membrane (PM) rich in sphingomyelin (SM) and cholesterol (Chol), provide a dynamic platform for a multitude of cellular functions. Rafts support the compartmentalization of cellular processes at the PM and are involved for example in signal transduction and membrane trafficking. Additionally, it has been proposed that rafts play an important role during cellular entry of a wide range of viruses, bacteria and toxins, as well as to serve as a platform for viral assembly and Alzheimer amyloid formation.

A range of proteins capable to bind to SM or Chol have been reported. Among them, actinoporins represent a well-studied group of widely distributed pore forming toxins (PFT) produced by a large number of sea anemone species. The crystal structure revealed the presence of a β-sandwich core flanked by two helices. Recently, we reported the isolation and characterization of a structurally homologous protein from mushroom exhibiting the typical actinoporin fold. Recent progress focusing on the sphingolipid head group binding site and the importance of cholesterol for membrane attachment based on point mutation results and molecular dynamics simulations will be discussed.