Receiving an asialoglycoprotein, and delivering the asialoglycoprotein into the cell via endocytosis. An asialoglycoprotein is a plasma glycoproteins from which the terminal sialic acid residue on their complex carbohydrate groups has been removed. The asialoglycoprotein receptor recognizes the terminal galactose and N-acetylgalactosamine units of the asialoglycoprotein, the receptor-ligand complex is internalized and transported to a sorting organelle where disassociation occurs before the receptor is recycled to the cell membrane.
A cDNA clone isolated from a lambda gt11 expression library of teratocarcinoma OTT6050 specifies for a glycoprotein with a molecular weight of about 44,000. The new glycoprotein was termed heparin binding protein-44 (HBP-44), since it was absorbed to a heparin-agarose column and was eluted from it by a buffer containing 1.5 M NaCl. HBP-44 mRNA was intensely expressed in PYS-2 parietal endoderm cells and in the kidney, and the RNA level increased about 10-fold during differentiation of F9 embryonal carcinoma cells to parietal endoderm cells. From the cDNA sequence, HBP-44 was concluded to be rich in charged amino acids, and large segments of the protein appeared to form alpha-helixes. The protein was considered to be anchored to the membrane by a cluster of hydrophobic amino acids present in the N-terminal region. Indeed, the N-terminal sequence of HBP-44 was homologous to asialoglycoprotein receptor, which is anchored to the membrane by the N-terminal region. Furthermore, a portion of the N-terminal region of HBP-44 was homologous to the leucine zipper domain. Except for the N-terminal region, HBP-44 had over-all homology with structural proteins such as myosin heavy chain. We propose that HBP-44 is extruded from plasma membranes and interacts with heparin and related molecules and that it is involved in the interactions of plasma membranes with basement membranes.
Interacting selectively and non-covalently with heparin, any member of a group of glycosaminoglycans found mainly as an intracellular component of mast cells and which consist predominantly of alternating alpha-(1->4)-linked D-galactose and N-acetyl-D-glucosamine-6-sulfate residues.
Wnt co-receptors LRP5 and LRP6 are two members of the low-density lipoprotein receptor family. Receptor-associated protein is not only a specialized chaperone but also a universal antagonist for members of the low-density lipoprotein receptor family. Here we test whether Mesd, a newly identified chaperone for members of the low-density lipoprotein receptor family, also binds to mature receptors at the cell surface and antagonizes ligand binding. We found that Mesd binds to cell surface LRP5 and LRP6, but not to other members of the low-density lipoprotein receptor family. Scatchard analysis revealed that Mesd binds cell surface LRP6 with high affinity (K(d) approximately 3.3 nM). Interestingly, the C-terminal region of Mesd, which is absent in sequences from invertebrates, is necessary and sufficient for binding to mature LRP6, and is required for LRP6 folding. We also found that LRP6 is not a constitutively active endocytosis receptor and binding of the receptor-associated protein to LRP6 partially competes for Mesd binding. Finally, we demonstrated that Mesd antagonizes ligand binding to LRP6 at the cell surface. Together our results show that in addition to serving as a folding chaperone, Mesd can function as a receptor antagonist by inhibiting ligand binding to mature LRP6.
J. Biol. Chem. 269, 23268-23273 (1994)[PubMed:8083232]
A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.
The multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) forms a complex with a receptor-associated protein (RAP) within the secretory pathway. RAP inhibits ligand binding to LRP and is required for normal functional expression of LRP in vivo, suggesting a physiological function as a specialized chaperone. We have used RAP-deficient mice, generated by gene targeting, to investigate the role of RAP in the biosynthesis and biological activity of LRP and other members of the LDL receptor gene family in various organs and in embryonic fibroblasts. Our results demonstrate that RAP is required for the proper folding and export of the receptors from the endoplasmic reticulum (ER) by preventing the premature binding of co-expressed ligands. Overexpression of apolipoprotein E (apoE), a high affinity ligand for LRP, results in dramatically reduced cellular LRP expression, an effect that is prevented by co-expression of RAP. RAP thus defines a novel class of molecular chaperones that selectively protect endocytic receptors by binding to newly synthesized receptor polypeptides, thereby preventing ligand-induced aggregation and subsequent degradation in the ER.
J. Biol. Chem. 269, 23268-23273 (1994)[PubMed:8083232]
A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.
J. Biol. Chem. 269, 23268-23273 (1994)[PubMed:8083232]
A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.
Amyloid beta-peptide (Abeta) deposition in cerebral vessels contributes to cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD). Here, we report that in AD patients and two mouse models of AD, overexpression of serum response factor (SRF) and myocardin (MYOCD) in cerebral vascular smooth muscle cells (VSMCs) generates an Abeta non-clearing VSMC phenotype through transactivation of sterol regulatory element binding protein-2, which downregulates low density lipoprotein receptor-related protein-1, a key Abeta clearance receptor. Hypoxia stimulated SRF/MYOCD expression in human cerebral VSMCs and in animal models of AD. We suggest that SRF and MYOCD function as a transcriptional switch, controlling Abeta cerebrovascular clearance and progression of AD.
J. Biol. Chem. 269, 23268-23273 (1994)[PubMed:8083232]
A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.
Negative regulation of very-low-density lipoprotein particle clearancedefinition[GO:0010916]
Any process that decreases the rate, frequency or extent of very-low-density lipoprotein particle clearance. Very-low-density lipoprotein particle clearance is the process in which a very-low-density lipoprotein particle is removed from the blood via receptor-mediated endocytosis and its constituent parts degraded.
J. Biol. Chem. 269, 23268-23273 (1994)[PubMed:8083232]
A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.
The process of assisting in the covalent and noncovalent assembly of single chain polypeptides or multisubunit complexes into the correct tertiary structure.
The multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) forms a complex with a receptor-associated protein (RAP) within the secretory pathway. RAP inhibits ligand binding to LRP and is required for normal functional expression of LRP in vivo, suggesting a physiological function as a specialized chaperone. We have used RAP-deficient mice, generated by gene targeting, to investigate the role of RAP in the biosynthesis and biological activity of LRP and other members of the LDL receptor gene family in various organs and in embryonic fibroblasts. Our results demonstrate that RAP is required for the proper folding and export of the receptors from the endoplasmic reticulum (ER) by preventing the premature binding of co-expressed ligands. Overexpression of apolipoprotein E (apoE), a high affinity ligand for LRP, results in dramatically reduced cellular LRP expression, an effect that is prevented by co-expression of RAP. RAP thus defines a novel class of molecular chaperones that selectively protect endocytic receptors by binding to newly synthesized receptor polypeptides, thereby preventing ligand-induced aggregation and subsequent degradation in the ER.
A cellular transport process in which transported substances are moved in membrane-bounded vesicles; transported substances are enclosed in the vesicle lumen or located in the vesicle membrane. The process begins with a step that directs a substance to the forming vesicle, and includes vesicle budding and coating. Vesicles are then targeted to, and fuse with, an acceptor membrane.
The multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) forms a complex with a receptor-associated protein (RAP) within the secretory pathway. RAP inhibits ligand binding to LRP and is required for normal functional expression of LRP in vivo, suggesting a physiological function as a specialized chaperone. We have used RAP-deficient mice, generated by gene targeting, to investigate the role of RAP in the biosynthesis and biological activity of LRP and other members of the LDL receptor gene family in various organs and in embryonic fibroblasts. Our results demonstrate that RAP is required for the proper folding and export of the receptors from the endoplasmic reticulum (ER) by preventing the premature binding of co-expressed ligands. Overexpression of apolipoprotein E (apoE), a high affinity ligand for LRP, results in dramatically reduced cellular LRP expression, an effect that is prevented by co-expression of RAP. RAP thus defines a novel class of molecular chaperones that selectively protect endocytic receptors by binding to newly synthesized receptor polypeptides, thereby preventing ligand-induced aggregation and subsequent degradation in the ER.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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