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PMID:12401114

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Citation

Di Jeso, B, Ulianich, L, Pacifico, F, Leonardi, A, Vito, P, Consiglio, E, Formisano, S and Arvan, P (2003) Folding of thyroglobulin in the calnexin/calreticulin pathway and its alteration by loss of Ca2+ from the endoplasmic reticulum. Biochem. J. 370:449-58

Abstract

During its initial folding in the endoplasmic reticulum (ER), newly synthesized thyroglobulin (Tg) is known to interact with calnexin and other ER molecular chaperones, but its interaction with calreticulin has not been examined previously. In the present study, we have investigated the interactions of endogenous Tg with calreticulin and with several other ER chaperones. We find that, in FRTL-5 and PC-Cl3 cells, calnexin and calreticulin interact with newly synthesized Tg in a carbohydrate-dependent manner, with largely overlapping kinetics that are concomitant with the maturation of Tg intrachain disulphide bonds, preceding Tg dimerization and exit from the ER. Calreticulin co-precipitates more newly synthesized Tg than does calnexin; however, using two different experimental approaches, calnexin and calreticulin were found in ternary complexes with Tg, making this the first endogenous protein reported in ternary complexes with calnexin and calreticulin in the ER of live cells. Depletion of Ca(2+) from the ER elicited by thapsigargin (a specific inhibitor of ER Ca(2+)-ATPases) results in retention of Tg in this organelle. Interestingly, thapsigargin treatment induces the premature exit of Tg from the calnexin/calreticulin cycle, while stabilizing and prolonging interactions of Tg with BiP (immunoglobulin heavy chain binding protein) and GRP94 (glucose-regulated protein 94), two chaperones whose binding is not carbohydrate-dependent. Our results suggest that calnexin and calreticulin, acting in ternary complexes with a large glycoprotein substrate such as Tg, might be engaged in the folding of distinct domains, and indicate that lumenal Ca(2+) strongly influences the folding of exportable glycoproteins, in part by regulating the balance of substrate binding to different molecular chaperone systems within the ER.

Links

PubMed PMC1223171 Online version:10.1042/BJ20021257

Keywords

Animals; Calcium/metabolism; Calnexin/chemistry; Calnexin/metabolism; Calreticulin/chemistry; Calreticulin/metabolism; Cell Line; Endoplasmic Reticulum/metabolism; Golgi Apparatus/metabolism; Kinetics; Protein Binding; Protein Folding; Rats; Thyroglobulin/biosynthesis; Thyroglobulin/chemistry; Thyroglobulin/metabolism

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

RAT:THYG

located_in

GO:0005783: endoplasmic reticulum

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

RAT:THYG

enables

GO:0042802: identical protein binding

ECO:0000353: physical interaction evidence used in manual assertion

RGD:3848

F

Seeded From UniProt

complete

RAT:THYG

enables

GO:0044877: protein-containing complex binding

ECO:0000353: physical interaction evidence used in manual assertion

RGD:2266
RGD:620288

F

Seeded From UniProt

complete

RAT:THYG

part_of

GO:0032991: protein-containing complex

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

RAT:CALX

located_in

GO:0005783: endoplasmic reticulum

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

RAT:CALX

part_of

GO:0032991: protein-containing complex

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

RAT:CALR

part_of

GO:0032991: protein-containing complex

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

See also

References

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