Low-density lipoprotein receptor structure and folding

Gent, Jürgen; Braakman, Ineke

doi:10.1007/s00018-004-4090-3

Cited by 102 publications

(95 citation statements)

References 92 publications

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“…This provided the first evidence that LDL-associated hormonally inactive DHEA-FAE can act as a source of biologically active hormones. The LDL receptor belongs to a family of structurally and functionally related cell surface receptors, most of which can bind and internalize LDL (10,21,34). Therefore, although the LDL receptor is highly expressed in lipoprotein-starved human fibroblasts and also abundant in HeLa cells, we cannot exclude the possibility that additional members of the LDL receptor family may take part in the internalization.…”

Section: Discussionmentioning

confidence: 98%

Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Wang

Wang²,

Wähälä³

et al. 2008

American Journal of Physiology-Endocrinology and Metabolism

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H]DHEA-FAE entered cells via LDL receptor or LDL receptorrelated receptor-mediated uptake, followed by intracellular hydrolysis and further metabolism into 5␣-adione and 4-adione that were excreted from cells. Although LAL contributed to the deesterification of DHEA-FAE, it was not solely responsible for the hydrolysis. ribonucleic acid interference; chromatography; dehydroepiandrosterone STEROID FATTY ACYL ESTERS (FAE) such as 17␤-estradiol-FAE (E 2 -FAE) and dehydroepiandrosterone-FAE (DHEA-FAE) belong to a unique family of naturally occurring hydrophobic hormone derivatives (15, 16). These steroids are esterified in a reaction catalyzed by plasma lecithin-cholesterol acyltransferase associated with high-density lipoprotein (HDL) particles and transported to other lipoprotein particles (14,18,30,35,42). The physiological role of steroid-FAE remains unclear. E 2 -FAE have been considered as the storage form of active estrogen in lipoproteins and adipose tissues that may be released as an active unconjugated hormone (3). It has also been suggested that E 2 -FAE may act as an antioxidant, protecting lipoproteins against oxidation (17, 41). Our previous studies (4) in a cell culture model demonstrated that lipoprotein-associated E 2 -FAE can be transferred into target cells and hydrolyzed to free E 2 .Compared with E 2 -FAE that is present in picomolar concentration in the circulation, nanomolar concentrations of circulating DHEA-FAE have been reported (7,26). Moreover, its hydrolysis product, DHEA, is one of the relatively abundant adrenal steroids secreted in humans and the precursor of estrogens and androgens (24). In blood, Ͼ90% of DHEA-FAE is associated with lipoproteins (38, 39). We are interested in the intracellular hydrolysis and metabolic fate of lipoproteinbound DHEA-FAE in target tissues.In postmenopausal women, only trace amounts of E 2 are present in serum, the overwhelming majority of estradiol residing in adipose tissue, mostly in the form of FAE (3). This finding opens up the possibility that adipose tissue could constitute a reservoir of many other steroid-FAEs from which active steroid hormones could, in principle, be liberated by hydrolysis of the FAE bond. Therefore, we aimed at exploring possible hydrolytic mechanisms involved in generating free DHEA and identifying potential bioactive metabolites of DHEA generated in cells. Lysosomal acid lipase (LAL) is the enzyme responsible for the intracellular hydrolysis of LDLassociated cholesteryl esters (cholesteryl-FAE) that are taken up by LDL-receptor-mediated endocytosis (12). Because of the similar ring structure of DHEA and cholesterol, we investigated the possibility that DHEA-FAE is also hydrolyzed by LAL. We chose HeLa cells as a model to study the hydrolysis and metabolism of LDL-associated DHEA-FAE because these cells, derived from the reproductive tract, have previously been useful in the study cholesterol metabolism (19,22,37). Moreover, HeLa cells express LAL mRNA (1) and RNA silencing works very reproducibly in these cells. Thus we inv...

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Section: Discussionmentioning

confidence: 98%

Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Wang

Wang²,

Wähälä³

et al. 2008

American Journal of Physiology-Endocrinology and Metabolism

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“…They were originally found to function as receptors, regulating the concentration of their ligands by binding and endocytosis (2), but they also play an increasingly recognized role in signal transduction, coupling cargo transport to signaling (3,4). The LDL receptor family has a modular structure, containing an assortment of LDL-A repeats, epidermal growth factor (EGF)-like repeats with ␤-propeller, a single transmembrane domain, and a small cytosolic tail (5)(6)(7).…”

mentioning

confidence: 99%

Calcium as a Crucial Cofactor for Low Density Lipoprotein Receptor Folding in the Endoplasmic Reticulum

Pena¹,

Jansens²,

Zadelhoff

et al. 2010

Journal of Biological Chemistry

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The family of low density lipoprotein (LDL) receptors mediate uptake of a plethora of ligands from the circulation and couple this to signaling, thereby performing a crucial role in physiological processes including embryonic development, cancer development, homeostasis of lipoproteins, viral infection, and neuronal plasticity. Structural integrity of individual ectodomain modules in these receptors depends on calcium, and we showed before that the LDL receptor folds its modules late after synthesis via intermediates with abundant non-native disulfide bonds and structure. Using a radioactive pulsechase approach, we here show that for proper LDL receptor folding, calcium had to be present from the very early start of folding, which suggests at least some native, essential coordination of calcium ions at the still largely non-native folding phase. As long as the protein was in the endoplasmic reticulum (ER), its folding was reversible, which changed only upon both proper incorporation of calcium and exit from the ER. Coevolution of protein folding with the high calcium concentration in the ER may be the basis for the need for this cation throughout the folding process even though calcium is only stably integrated in native repeats at a later stage.

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“…The mature LDLR is a singlepass transmembrane, multidomain glycoprotein of 839 residues that comprises seven different regions (see Fig. 1): seven tandem LDLR type A (LA) modules at the N terminus responsible for binding of lipoproteins, two epidermal growth factor (EGF) repeats, a YWTD domain, another EGF-like repeat, an O-linked glycosylation region, a transmembrane segment, and a C-terminal cytoplasmic tail (4).…”

mentioning

confidence: 99%

Scrambled Isomers as Key Intermediates in the Oxidative Folding of Ligand Binding Module 5 of the Low Density Lipoprotein Receptor

Arias-Moreno

Arolas

Aviles

et al. 2008

Journal of Biological Chemistry

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The ligand binding module five (LA5) of the low density lipoprotein receptor is a small, single-domain protein of 40 residues and three disulfide bonds with a calcium binding motif that is essential for its structure and function. Several mutations in LA5 have been reported to cause familial hypercholesterolemia by impairing a proper folding of the module. The current study reports the oxidative folding and reductive unfolding pathways of wild type and mutant LA5 modules through kinetic and structural analysis of the trapped intermediates. Wild type LA5 folding involves an initial phase of nonspecific packing where the sequential oxidation of its cysteines gives rise to complex equilibrated populations of intermediates. In the presence of calcium, the attainment of a coordination-competent conformation becomes the rate-limiting step of folding while binding of the ion funnels both thermodynamically and kinetically the folding reaction toward the native state. In the absence of calcium, a scrambled isomer (termed Xa) constitutes the global free energy minimum of the folding process. Xa and the native form are stable, inter-convertible species whose relative populations at equilibrium appear displaced in disease-linked mutants toward the scrambled form. Because stable scrambled isomers such as Xa avoid the exposition of reactive cysteines in misfolded modules, they might constitute a strategy to prevent wrong interactions with other domains during folding of the receptor. Comparison of the folding pathways of wild type and mutant LA5 provides the molecular basis to understand how LA modules fold into a functional conformation or upon mutation misfold and lead to disease.

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Low-density lipoprotein receptor structure and folding

Cited by 102 publications

References 92 publications

Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Calcium as a Crucial Cofactor for Low Density Lipoprotein Receptor Folding in the Endoplasmic Reticulum

Scrambled Isomers as Key Intermediates in the Oxidative Folding of Ligand Binding Module 5 of the Low Density Lipoprotein Receptor

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