Toon de Kroon
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3584 CH Utrecht,
Phone: +31 (0)30 253 3424
Group of Toon de Kroon
MEMBRANE LIPID HOMEOSTASIS
Membrane lipid composition determines the physical properties of biological membranes that are crucial for maintaining the membrane barrier and for the functioning of membrane proteins. Research in the group is aimed at understanding the principles that govern bulk membrane lipid composition and at identifying the underlying sensor-effector modules. The following topics are investigated in the model eukaryote S. cerevisiae using biochemical, molecular biological, genetic and chemical biological approaches.
Interplay between membrane lipid class and acyl chain composition
By gradually reducing the content of phosphatidylcholine (PC) from 40 % to below 1% of total membrane phospholipids we identified a novel regulatory mechanism for membrane lipid composition in yeast. The loss of the bilayer lipid PC is compensated for by a rise in the non-bilayer preferring lipid phosphatidylethanolamine (PE). Mass spec analysis revealed that PC depletion is accompanied by dramatic changes in the acyl chain composition of PE that reduce its non-bilayer propensity. Thus, the intrinsic membrane curvature of the membranes is maintained in the optimal range. The current challenge in the project of Xue Bao is to elucidate the underlying sensing mechanism and regulatory network. Conversely, by overexpressing the G-3-P acyltransferase Sct1 the level of saturated acyl chains is increased which impacts lipid class composition. Mike Renne is addressing the role of acyltransferases in the regulation of lipid acyl chain desaturation.
Metabolism of phospholipids at the molecular species level
Pulse labeling with stable isotope-labeled precursors and subsequent analysis of phospholipid species by ESI-MS/MS demonstrated the occurrence of PC remodeling by acyl chain exchange. We now want to identify the phospholipases and acyltransferases involved, with the ultimate aim of solving the function of PC remodeling. In a related project funded by the Barth Syndrome Foundation the acyl chain remodeling of the mitochondrial lipid cardiolipin by the transacylase Taz1p is investigated. Manipulation of the acyl chain composition of yeast by overexpression of the G-3-P acyltransferase Sct1 is an important tool in these projects.
Lipid engineering to increase the tolerance of yeast for organic solvents
By partitioning into cellular membranes organic solvents impact on lipid packing, membrane fluidity, and ultimately on membrane barrier function. The goal of Amrah Weijn's project is to improve the tolerance of yeast to organic solvents by engineering the membrane lipid composition.
Structure-function analysis of the methyltransferase Opi3p
Opi3p is a 23 kD integral membrane protein of the ER that catalyzes the 2nd and 3rd methylation in the conversion of PE to PC. The catalytic mechanism and the membrane topology of this enzyme are being addressed.
Detection of lipid-protein interactions by photocrosslinking
New technology has been developed based on photocrosslinking and click chemistry for detecting lipid-protein interactions in a biological membrane of interest. Short chain lipid analogues mimicking PC equipped with a photoactivatable moiety attached to the headgroup and containing azide-modified acyl chains for detection by click chemistry, have been successfully used to identify established and potential new interaction partners of PC in yeast mitochondrial membranes.