1. Institute of Biology/Zoology, Free University of Berlin, Königin-Luise-Strasse 1−3, D-14 195 Berlin, Germany, Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, California 94609, USA, Protein Engineering Network of Centres of Excellence (PENCE), Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada