Novel covalent chaperone complexes associated with human chorionic gonadotropin beta subunit folding intermediates.
Molecular chaperones facilitate the folding of proteins in the endoplasmic reticulum (ER) of mammalian cells. The glycoprotein hormone chorionic gonadotropin beta subunit is a secretory protein whose folding in the ER has been demonstrated (Huth, J. R., Mountjoy, K., Perini, F., and Ruddon, R. W.(1992) J. Biol. Chem. 267, 8870-8879). Because folding of wild type hCG-beta subunit occurs in the ER with a t1/2 = 4-5 min, stable association of ER chaperones with hCG-beta have been difficult to detect probably because they have a short half-life. However, beta-chaperone complexes containing the ER chaperones BiP, ERp72, and ERp94 have been detected in slow folding mutants of hCG-beta subunit that lack both of the N-linked oligosaccharides (Feng, W., Matzuk, M. M., Mountjoy, K., Bedows, E., Ruddon, R. W., and Boime, I. (1995) J. Biol. Chem. 270, 11851-11859). The questions addressed here are 1) whether the detection of chaperone-containing complexes is related to the absence of carbohydrate or to the rate of hCG-beta subunit folding, 2) whether such complexes are dead-end or whether they lead to formation of a secreted, mature hCG-beta form, and 3) what the nature of the hCG-beta-chaperone binding is. The data obtained indicate that the amount of detectable hCG-beta-chaperone complexes correlates with the rate or extent of folding, that the complexes of hCG-beta with ER chaperones lead to the formation of secretable beta, and that the complexes of hCG-beta with chaperones involve the formation of intermolecular disulfide bonds.
Feng
W
W
The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA.
Bedows
E
E
Norton
S E
SE
Ruddon
R W
RW
D000818:Animals; D016466:CHO Cells; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D004220:Disulfides / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006207:Half-Life; D006801:Humans; D066298:In Vitro Techniques; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D015394:Molecular Structure; D009154:Mutation; D017510:Protein Folding; D014162:Transfection
D018997:Chorionic Gonadotropin, beta Subunit, Human; D004220:Disulfides; D018832:Molecular Chaperones