Deciphering Endosomal Recycling Pathways: Insights into Protein and Lipid Sorting in the Endo-Lysosomal System

• Applicant: Professor Dr. Florian Fröhlich
• Subject Area: Biochemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 534958928

Lysosomes and vacuoles play a crucial role in the degradation of intracellular and extracellular material. The function of lysosomes depends on two classes of proteins: soluble hydrolases and integral lysosomal membrane proteins. Lysosomal hydrolases require an acidic pH produced by vacuolar H+-ATPase and other ion channels, whereas membrane permeases export metabolites produced during lysosomal degradation. In particular, defects in endosomal recycling have been associated with lysosomal storage diseases and neurodegenerative disorders. To unravel the mechanisms underlying vacuolar/lysosomal targeting and protein and lipid sorting, we use yeast as a model organism. We will systematically investigate endosomal recycling pathways in yeast using our established quantitative proteomics approach. By integrating metabolic labeling, vacuole purification, and mass spectrometry-based proteomics, we will investigate cargo proteins, identify sorting motifs, and elucidate the functional role of endosomal recycling factors. In particular, we will focus on characterizing an unexplored protein called Ptm1, whose transport is affected by deletion of the Mvp1 and Gga proteins. Recent structural analyses suggest that Ptm1 is involved in endosomal recycling and may have lipid-binding properties. Our goal is to clarify key questions regarding the cargo spectrum, sorting motifs, and lipid regulation within the endo-lysosomal system. Systematic analysis of retrograde transport pathways and identification of cargo proteins will provide insights into the mechanisms of protein and lipid sorting. By studying the cellular function of Ptm1, we expect to uncover new aspects of endosomal recycling and its impact on the endo-lysosomal pathway. Together, this will contribute to a better understanding of endosomal homeostasis and its relevance to diseases associated with lysosomal dysfunction and neurodegeneration.

• DFG Programme: Research Grants