The role of two families of lipid droplet-associated proteins
by Siqi Sun
Date of Examination:2024-09-23
Date of issue:2025-09-16
Advisor:Prof. Dr. Till Ischebeck
Referee:Prof. Dr. Till Ischebeck
Referee:Prof. Dr. Jan de Vries
Persistent Address:
http://dx.doi.org/10.53846/goediss-11495
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Abstract
English
Lipid droplets (LDs) are unique subcellular compartments that are specialized for lipid storage. In recent years, the number of identified and characterized LD-associated proteins has been greatly increased, which, on the one hand, greatly expanded our understanding of the LD functions, making the LDs being increasingly recognized as an organelle involved in various biological processes. On the other hand, it raises important questions about how the LD-associated proteins are brought to the LD surface, and what the functions of the uncharacterized LD proteins are. Due to the unique LD structure, a hydrophobic core enclosed by a phospholipid monolayer, LD proteins need to involve architectures other than the classical transmembrane domains for LD targeting. So far, two structural features, a hydrophobic domain and an amphipathic helix, have been found to play key roles in LD targeting. However, these two features cannot cover all the LD targeting situations, as they are not observed in many identified LD proteins. In our study, we brought new insights into the structural features for LD targeting using a combined method of molecular dynamic (MD) simulations with cell biological approaches. With the combined method, we investigated the physiochemical and structural features can be critical for LD targeting and successfully unveiled the LD targeting regions of seven recently identified Arabidopsis LD proteins. Among them, five proteins possess a potential hydrophobic/amphipathic helix responsible for LD targeting. In addition, we also suggested a different targeting mechanism for CALEOSIN1. Furthermore, we reported a new structural feature, a hydrophobic surface region, that is highly likely to serve as an LD targeting site for CALEOSIN1, LD LIPASE (LIDL1), LD-ASSOCIATED HYDROLASE 1 (LDAH1) and CYCLOARTINOL SYNTHASE 1 (CAS1). Moreover, we also found proteins with more than one LD targeting sites that can work independently from each other. In this thesis, we also initialized characterization of two recently identified protein families, the LDAH and LD-ASSOCIATED DEHYDROGENASE (LDDH) protein families. To investigate their potential physiological functions, we applied different techniques to screen for potential phenotypes and tested the enzymatic activities of LDAH proteins. Our results suggested that LDAH1 and LDAH2 proteins are GXSXG lipases and are likely to serve as DAG hydrolases. Overall, in this study, we investigated the LD targeting regions of a list of known LD proteins, and contributed to the understanding of LD targeting mechanism. Besides, we also brought new insights into the role of LDAH protein family. Apart from my main topic, I also participated in investigating the SEED LIPID DROPLET PROTEIN (SLDP) - LIPID DROPLET PLASMA MEMBRANE ADAPTOR (LIPA) complex which tethers LDs to the plasma membrane, the role of an LD protein (ERD7) upon drought stress, as well as the investigation of LD-related molecular programs in stress response in an algae species Mesotaenium.
Keywords: Lipid Droplet Protein; Arabidopsis thaliana
