39-kDa receptor-associated protein (RAP) facilitates secretion and ligand binding of extracellular region of very-low-density-lipoprotein receptor: implications for a distinct pathway from low-density-lipoprotein receptor.
We have expressed the extracellular regions of the low-density-lipoprotein (LDL) receptor and the very-low-density-lipoprotein (VLDL) receptor, along with the full-length forms of the receptors, in insect cells in a baculovirus system. The extracellular region of the LDL receptor has been secreted successfully into the culture medium, and it retained the capacities of binding 125I-labelled LDL and beta-VLDL. In contrast, the extracellular region of the VLDL receptor remained intracellular and it did not bind 125I-beta-VLDL. This difference in expression behaviour between the homologous regions of the two receptors suggests that the two receptor systems are different in receptor-protein maturation or protein targeting. Next we developed the co-expression system with 39-kDa receptor-associated protein (RAP). This co-expression facilitated the secretion of the extracellular region of the VLDL receptor into the culture medium and the secreted receptor bound 125I-beta-VLDL. The VLDL receptor remaining intracellular that was co-expressed with RAP also showed binding capacity to 125I-beta-VLDL, implying that the existence of RAP prevented receptor-protein aggregation or improved protein-folding status of the truncated VLDL receptor. On the other hand, expression of the extracellular region of the LDL receptor was not facilitated by RAP co-expression. Thus RAP plays an essential role in maintenance of the active conformation and secretion of the extracellular region of the VLDL receptor.
Department of Molecular Biology, Biomolecular Engineering Research Institute, 6-2-3 Furuedai, Suita-City, Osaka 565-0874, Japan.
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A
Sato
Y
Y
Shimada
J
J
Herz
T
T
Yamamoto
H
H
Jingami
D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D007313:Insecta; D026563:LDL-Receptor Related Protein-Associated Protein; D008024:Ligands; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D002352:Carrier Proteins; D006023:Glycoproteins; D026563:LDL-Receptor Related Protein-Associated Protein; D008024:Ligands; D018832:Molecular Chaperones; D011973:Receptors, LDL; C036053:VLDL receptor