Hydrophobic and Basic Domains Target Proteins to Lipid Droplets

Abstract

In recent years, progress in the study of the lateral organization of the plasma membrane has led to the proposal that mammalian cells use two different organelles to store lipids: intracellular lipid droplets (LDs) and plasma membrane caveolae. Experimental evidence suggests that caveolin (CAV) may act as a sensitive lipid-organizing molecule that physically connects these two lipid-storing organelles. Here, we determine the sequences necessary for efficient sorting of CAV to LDs. We show that targeting is a process cooperatively mediated by two motifs. CAV's central hydrophobic domain (Hyd) anchors CAV to the endoplasmic reticulum (ER). Next, positively charged sequences (Pos-Seqs) mediate sorting of CAVs into LDs. Our findings were confirmed by identifying an equivalent, non-conserved but functionally interchangeable Pos-Seq in ALDI, a bona fide LD-resident protein. Using this information, we were able to retarget a cytosolic protein and convert it to an LD-resident protein. Further studies suggest three requirements for targeting via this mechanism: the positive charge of the Pos-Seq, physical proximity between Pos-Seq and Hyd and a precise spatial orientation between both motifs. The study uncovers remarkable similarities with the signals that target proteins to the membrane of mitochondria and peroxisomes

Insertion of perilipin 3 into a glycero(phospho)lipid monolayer depends on lipid headgroup and acyl chain species

“…For caveolins, it was shown that a cationic domain close to a hydrophobic region is required to sort the protein to LDs in the endoplasmic reticulum (21). Attaching these domains to non-LD binding proteins conferred to them LD localization (21).…”

“…The perilipins are synthesized on cytosolic ribosomes (18)(19)(20) and are thus sorted to the LD interface in a different manner than those proteins that originate from the endoplasmic reticulum, such as caveolin, for example (21). Sorting of caveolin is cooperatively mediated by a dual motif consisting of a hydrophobic sequence located close to a positively charged sequence (21). Targeting has been investigated for perilipins 1 through 5 in cellular studies and different regions of the proteins have been identified (1,(22)(23)(24)(25)(26)(27).…”

Zitosoleko lipido-tanten sorrera eta erabilera

“…LTetarako eta LTetatiko proteinen trafikoari buruzko ikerkuntza asko egin diren arren, prozesu horien ezagumenduak hutsune asko dauzka. Proteinak LTetara biderarazten dituen zenbait aminoazido-sekuentzia labur identifikatu da [8,9]. Sekuentzia horiek urkila hidrofobiko bat edukitzen dute helize kationiko edo anfipatiko baten alboan.…”

Hepatitis C virus NS4B targets lipid droplets through hydrophobic residues in the amphipathic helices

“…Although several cellular and viral proteins localize on the LD membrane, consensus signals for LD targeting are not defi ned ( 1 ). Recent reports have shown that LD-targeting activity resides in amphipathic helices (19)(20)(21)(22)(23) or in hydrophobic regions (24)(25)(26).…”