Function and regulation of endocytic sorting factors

In the process of endocytosis, cells can generate vesicles at the limiting plasma membrane to internalize receptors, bound ligands and other cargo. This is best studied for clathrin-mediated endocytosis, during which more than 50 different factors and their spatially and temporally controlled interplay generate endocytic clathrin-coated vesicles. We study key factors of the underlying machinery such as AP-2, CALM (PICALM) and NECAP to explore their function and we address the question of how the individual factors are controlled, e.g. by reversible posttranslational modifications. Very recently we showed that blocking expression of AP-2 and thus inhibition of clathrin-mediated endocytosis leads to altered expression of more than 1000 proteins among the plasma membrane proteome (Tobys et al., 2020).

Deciphering the molecular defects of the Hermansky-Pudlak-Syndrome (HPS)

HPS is a rare autosomal recessive genetic disorder that is characterized by symptoms including oculocutaneous hypopigmentation/albinism, a bleeding diathesis and the lysosomal accumulation of ceroid lipofuscin. Ten different genes are currently known to cause HPS, and two of these identified genes code of subunits of the so-called AP-3 complex. AP-3 mediates intracellular sorting of proteins in endosomes, however much of its precise function and regulation in different tissues and specialized cells remains unknown. We therefore address these issues together with colleagues from the Department of Human Genetics and the Center for Pediatrics. Ultimately, we hope to contribute to a better understanding of the disease and to pave the way to new causative therapies.

Surface-Plasmon-Resonance (SPR) biosensor based analysis of biomolecular interactions

SPR-based analysis of molecular interactions is a versatile and rapid technology for in vitro studies under defined conditions. We have more than 20 years of experience in the SPR analysis of protein-protein interactions, as well as interactions of proteins with immobilized liposomal membranes. Currently we use a BIAcore T200 (Cytiva, formerly GE Healthcare), which allows to work with small sample numbers in manual runs, or automated analysis of hundreds of probes. We offer the technology to anybody interested as part of a joined collaboration. Our experience is documented in numerous publications (e.g. Höning et al., Mol Cell, 2005; Miller et al., Cell 2011; Hackmann et al., PNAS 2013; Wrobel et al., Dev Cell 2019).

Biogenesis and turnover of lipid droplets

Any known cell is able to store triacylglcerol (TAG) in intracellular lipid droplets (LDs), but three cell types are professional in this aspect: adipocytes or white and brown adipose tissue and hepatocytes. In contrast to any other intracellular organelle, the hydrophobic core of LDs is surrounded by a phospholipid monolayer. This has far-reaching implications ranging from biosynthesis of LDs, the exchange of molecules, LD turnover to their contact with other organelles. The LD phospholipid monolayer is decorated with a several proteins and we characterized PLIN3 (TIP47) recruitment from the cytosol to LDs and showed altered incorporation of TAG into LDs in PLIN3 knock-down cells (Bulankina et al., J Cell Biol., 2009). Despite this knowledge, the precise function of PLIN3 in “resting” and TAG-incorporating cells remains to be uncovered. We address these issues and are further interested in the association of LDs with organelles of the endomembrane system.