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TIP47 functions in the biogenesis of lipid droplets

¹ Institute for Biochemistry II and ² Department of Molecular Structural Biology, University of Göttingen, 37073 Göttingen, Germany
³ Institute for Biochemistry I and ⁴ Cologne Center for Molecular Medicine, University of Cologne, 50931 Cologne, Germany
⁵ Department of Neurobiology, Max-Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
⁶ Section Endocrinology and Metabolism, Faculty of Science and Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, Netherlands

Correspondence to S. Höning: shoening{at}uni-koeln.de

TIP47 (tail-interacting protein of 47 kD) was characterized as a cargo selection device for mannose 6-phosphate receptors (MPRs), directing their transport from endosomes to the trans-Golgi network. In contrast, our current analysis shows that cytosolic TIP47 is not recruited to organelles of the biosynthetic and endocytic pathways. Knockdown of TIP47 expression had no effect on MPR distribution or trafficking and did not affect lysosomal enzyme sorting. Therefore, our data argue against a function of TIP47 as a sorting device. Instead, TIP47 is recruited to lipid droplets (LDs) by an amino-terminal sequence comprising 11-mer repeats. We show that TIP47 has apolipoprotein-like properties and reorganizes liposomes into small lipid discs. Suppression of TIP47 blocked LD maturation and decreased the incorporation of triacylglycerol into LDs. We conclude that TIP47 functions in the biogenesis of LDs.

A.V. Bulankina's present address is InnerEarLab, Dept. of Otolaryngology and Center for Molecular Physiology of the Brain, University of Göttingen, 37075 Göttingen, Germany.

K. Mutenda's present address is Dept. of Biochemistry and Molecular Biology, University of Southern Denmark, 5230 Odense M, Denmark.

Abbreviations used in this paper: ADRP, adipose differentiation-related protein; apoE, apolipoprotein E; CatD, cathepsin D; DMPC, dimyristoyl-phosphatidylcholine; KD, knockdown; LD, lipid droplet; MPR, mannose 6-phosphate receptor; PNS, postnuclear supernatant; SPR, surface plasmon resonance; TAG, triacylglycerol.

© 2009 Bulankina et al.
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