| Structural highlights
Disease
LDLR_HUMAN Defects in LDLR are the cause of familial hypercholesterolemia (FH) [MIM:143890; a common autosomal semi-dominant disease that affects about 1 in 500 individuals. The receptor defect impairs the catabolism of LDL, and the resultant elevation in plasma LDL-cholesterol promotes deposition of cholesterol in the skin (xanthelasma), tendons (xanthomas), and coronary arteries (atherosclerosis).[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [:][32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43]
Function
LDLR_HUMAN Binds LDL, the major cholesterol-carrying lipoprotein of plasma, and transports it into cells by endocytosis. In order to be internalized, the receptor-ligand complexes must first cluster into clathrin-coated pits. In case of HIV-1 infection, functions as a receptor for extracellular Tat in neurons, mediating its internalization in uninfected cells.RXFP1_HUMAN Receptor for relaxins. The activity of this receptor is mediated by G proteins leading to stimulation of adenylate cyclase and an increase of cAMP. Binding of the ligand may also activate a tyrosine kinase pathway that inhibits the activity of a phosphodiesterase that degrades cAMP.
Publication Abstract from PubMed
The peptide hormone relaxin is showing potential as a treatment for acute heart failure. Although it is known that relaxin mediates its actions through the G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1), little is known about the molecular mechanisms by which relaxin binding results in receptor activation. Previous studies have highlighted that the unique N-terminal low density lipoprotein class A (LDLa) module of RXFP1 is essential for receptor activation, and it has been hypothesized that this module is the true "ligand" of the receptor that directs the conformational changes necessary for G protein coupling. In this study, we confirmed that an RXFP1 receptor lacking the LDLa module binds ligand normally but cannot signal through any characterized G protein-coupled receptor signaling pathway. Furthermore, we comprehensively examined the contributions of amino acids in the LDLa module to RXFP1 activity using both gain-of-function and loss-of-function mutational analysis together with NMR structural analysis of recombinant LDLa modules. Gain-of-function studies with an inactive RXFP1 chimera containing the LDLa module of the human LDL receptor (LB2) demonstrated two key N-terminal regions of the module that were able to rescue receptor signaling. Loss-of-function mutations of residues in these regions demonstrated that Leu-7, Tyr-9, and Lys-17 all contributed to the ability of the LDLa module to drive receptor activation, and judicious amino acid substitutions suggested this involves hydrophobic interactions. Our results demonstrate that these key residues contribute to interactions driving the active receptor conformation, providing further evidence of a unique mode of G protein-coupled receptor activation.
The relaxin receptor (RXFP1) utilizes hydrophobic moieties on a signaling surface of its N-terminal low density lipoprotein class A module to mediate receptor activation.,Kong RC, Petrie EJ, Mohanty B, Ling J, Lee JC, Gooley PR, Bathgate RA J Biol Chem. 2013 Sep 27;288(39):28138-51. doi: 10.1074/jbc.M113.499640. Epub, 2013 Aug 7. PMID:23926099[44]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
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- ↑ Ebhardt M, Schmidt H, Doerk T, Tietge U, Haas R, Manns MP, Schmidtke J, Stuhrmann M. Mutation analysis in 46 German families with familial hypercholesterolemia: identification of 8 new mutations. Mutations in brief no. 226. Online. Hum Mutat. 1999;13(3):257. PMID:10090484 doi:<257::AID-HUMU15>3.0.CO;2-A 10.1002/(SICI)1098-1004(1999)13:3<257::AID-HUMU15>3.0.CO;2-A
- ↑ Hattori H, Nagano M, Iwata F, Homma Y, Egashira T, Okada T. Identification of recurrent and novel mutations in the LDL receptor gene in Japanese familial hypercholesterolemia. Mutation in brief no. 248. Online. Hum Mutat. 1999;14(1):87. PMID:10447263 doi:<87::AID-HUMU14>3.0.CO;2-N 10.1002/(SICI)1098-1004(1999)14:1<87::AID-HUMU14>3.0.CO;2-N
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- ↑ Kong RC, Petrie EJ, Mohanty B, Ling J, Lee JC, Gooley PR, Bathgate RA. The relaxin receptor (RXFP1) utilizes hydrophobic moieties on a signaling surface of its N-terminal low density lipoprotein class A module to mediate receptor activation. J Biol Chem. 2013 Sep 27;288(39):28138-51. doi: 10.1074/jbc.M113.499640. Epub, 2013 Aug 7. PMID:23926099 doi:http://dx.doi.org/10.1074/jbc.M113.499640
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