The New Face of the Lipid Droplet: Lipid Droplet Proteins

Abstract

The lipid droplet (LD) is an organelle with vital functions found in nearly all organisms. LD proteomic research has provided fundamentally important insights into this organelle's functions. The review provides a summary of LD proteomic studies conducted across diverse organisms and cell and tissue types. The accumulated proteomic data are reviewed for evidence of a protein targeting mechanism for the organelle. The hypotheses for several specific localization mechanisms based on what is known about targeting mechanisms for other organelles and vesicles are provided. Although the nature of the mechanism is not known, the functional data demonstrate that the targeting mechanism and, indeed, the organelle itself, is conserved from prokaryotes to eukaryotes. It is hoped that the review will help inspire further research leading to novel discoveries in the field.

Adiposome Targeting and Enzymatic Activity of Lipid Droplet-Specific Proteins

“…While an understanding of the functions of the LD as an organelle is still developing, it is certain that it plays a significant role in energy homeostasis, in particular lipid metabolism, storage, and transportation (Bartz et al, 2007a;Liu et al, 2004;Walther et al, 2017;Yao et al, 2019). Proteomic and lipidomic studies using isolated LDs have provided detailed information on the protein and lipid composition of the organelle from almost all model organisms (Liu et al, 2004;Zhang and Liu, 2019). Many of the LD proteins identified through proteomics have also been studied in morphological and functional studies (Ding et al, 2012;Liu et al, 2004;Na et al, 2015).…”

“…Most LD-associated proteins are found at multiple locations in cells. However, a smaller number are resident proteins that specifically and directly localize on the organelle Ohsaki et al, 2014;Wolins et al, 2006;Zhang and Liu, 2019). With few exceptions these proteins are only found on the LD surface, and therefore it is believed that they possess the binding mechanism(s) specific for monolayer phospholipid membranes, the nature of which is under debate.…”

“…Several studies have attempted to identify targeting mechanisms with limited success (Walther and Farese, 2012). Based on these findings targeting mechanisms can be roughly divided into two groups, direct and indirect (Zhang and Liu, 2019). Indirect localization is mainly maintained by acylation and protein-protein interaction (Leung et al, 2007;Shen et al, 2009).…”

Identification of Functional Noncoding RNA-encoded Proteins on Lipid Droplets

“…Lipid droplet (LD) is a ubiquitous intracellular organelle containing a neutral lipid core bounded by phospholipid monolayer membrane and some integral and peripheral membrane proteins(13, 14). LDs play critical roles in lipid storage, transport and metabolism(15-17). Abnormal LD dynamics is related to the cause and development of metabolic diseases, such as obesity, atherosclerosis, fatty liver disease, and type 2 diabetes(17-19).…”

“…LDs play critical roles in lipid storage, transport and metabolism(15-17). Abnormal LD dynamics is related to the cause and development of metabolic diseases, such as obesity, atherosclerosis, fatty liver disease, and type 2 diabetes(17-19). The LD-associated proteins are the main executors of LD function.…”