http://www.lipidprofiles.com/

Markus R WENK (Associate Professor)   Contact Information: Markus R. Wenk, PhD National University of Singapore Department of Biochemistry 8 Medical Drive, Block MD 7 Singapore 117597 T +65 (6516) 3624 F +65 (6779) 1453 email: bchmrw@nus.edu.sg Joint appointment : Department of Biochemistry and Department of Biological Sciences

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Research Interest
Cellular membranes share common classes of lipid constituents, but differ in the relative proportions of the individual molecular species. They segregate cellular compartments and provide a structural scaffold for the organization of enzymatic machineries and for the anchoring of the cytoskeleton. In addition, membrane lipids play an important role in cellular signaling. This signaling function is made possible by the very active metabolism of some lipids leading to the transient accumulation of compounds that play critical roles in short and long range cellular regulation. A well-known example of regulatory phospholipids are the phosphoinositides (phosphorylated derivatives of phosphatidylinositol) which contribute to the regulation of nearly every cellular function including membrane traffic, cell proliferation, and cell motility. Similar signaling functions are emerging for a number of other lipid classes, including ceramides, lysolipids, and diacylglycerols.

The critical role of lipids in cell, tissue and organismal physiology is demonstrated by a large number of genetic studies and by the many human diseases involving the disruption of lipid metabolic enzymes and pathways. Examples of such diseases include cancer, diabetes and neurodegenerative diseases. Surprisingly, so far, the explosion of information in the fields of genomics and proteomics has not been matched by a corresponding advancement of knowledge in the field of lipids. Conventional methods of lipid analysis are hampered by low sensitivity and the difficulty to detect and measure lipids from unprocessed extracts. Furthermore, many available techniques of lipid analysis have not been suited to systematic studies. We plan to capitalize on the increased sensitivity and resolution power of mass spectrometry to advance the field and obtain biologically and medically important information.

Enlarge
The inositol head group of phosphatidylinositol can be reversibly phosphorylated at various positions resulting in seven naturally occurring phosphoinositides. Shown here is the molecular structure of 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphatidylinositol-4,5-bisphosphate, an abundant PI(4,5)P2 species in mammalian cells. Commonly used methods for the detection of phosphoinositides include fluorescent techniques, receptor displacement assays and radiometric measurements of chromatographically separated products after metabolic labeling with radioisotope precursors. As a result, some of these approaches report the position of the phosphate(s) on the inositol headgroup (isomer information). Electrospray ionization mass spectrometry, on the other hand, reveals a number of PIP2 species with different fatty acid compositions, depending on the number of carbon atoms and double bonds in their fatty acid moieties. This fatty acid information adds an additional layer of information to phosphoinositide signaling. The dotted line indicates the plane of the bilayer and roughly marks the aqueous-to-hydrophobic boundary of the membrane.

Current Projects

'Lipidomics of neuronal membranes - Identification of lipids involved in neurosecretion and neurodegenerative diseases'
The goal of this project is to identify membrane lipids which undergo stimulation induced metabolism during neurosecretion. This work will be done in collaboration with research groups at the National University of Singapore, the University of Western Australia, Perth and Yale University in New Haven, CT, USA.

'Lipid profiling of Mycobacteria in different physiological states'
The aim of this project is to test whether tubercle bacilli change their membrane lipid composition upon entry into metabolically inert states which are resistant to conventional anti-tuberculosis treatment. Research collaboration with the Novartis Institute for Tropical Diseases, Singapore.

'Lipidomics of enveloped viruses - novel molecular insights into host-pathogen interactions'
Mass spectrometry will be used to determine the lipid inventory of enveloped viruses which will be the first systematic high resolution compositional analysis of viral envelope lipids. In collaboration with groups at the Institute for Molecular and Cell Biology, Singapore and Yale University, New Haven, CT, USA.

Selected Publications