Multimerization of bovine thyroglobulin, partially unfolded or partially unfolded/reduced; involvement of protein disulfide isomerase and glutathionylated disulfide linkage.
Fate of the nascent thyrolglobulin (Tg) molecule is characterized by multimerization. To establish the formation of Tg multimers, the partially unfolded/reduced Tg or deoxycholate-treated/ reduced Tg was subjected to protein disulfide isomerase (PDI)-mediated multimerization. Oxidized glutathione/PDI-mediated formation of multimeric Tg forms, requiring at least an equivalent molar ratio of PDI/Tg monomer, decreased with increasing concentration of reduced glutathione (GSH), suggesting the oxidizing role of PDI. Additional support was obtained when PDI alone, at a PDI/Tg molar ratio of 0.3, expressed a rapid multimerization. Independently, the exposure of partially unfolded Tg to GSH resulted in Tg multimerization, enhanced by PDI, according to thiol-disulfide exchange. Though to a lower extent, a similar result was observed with the dimerization of deoxycholate-pretreated Tg monomer. Consequently, it is implied that intermolecular disulfide linkage may be facilitated at a limited region of unfolded Tg. In an attempt to examine the multimerization site, the cysteine residue-rich fragments of the Tg were subjected to GSH-induced multimerization; a 50 kDa fragment, containing three vicinal dithiols, was multimerized, while an N-terminal domain was not. Present results suggest that the oxidase as well as isomerase function of PDI may be involved in the multimerization of partially unfolded Tg or deoxycholate-treated Tg.
Liu
Xi-Wen
XW
College of Pharmacy, Chungnam National University, Yuseong-Ku, Taejon 305-764, Korea.
Sok
Dai-Eun
DE
D000818:Animals; D002417:Cattle; D004789:Enzyme Activation / Q000502:physiology; D019803:Glutathione Disulfide / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D019704:Protein Disulfide-Isomerases / Q000737:chemistry / Q000378:metabolism*; D017510:Protein Folding; D013954:Thyroglobulin / Q000737:chemistry / Q000378:metabolism*
D013954:Thyroglobulin; D019704:Protein Disulfide-Isomerases; D019803:Glutathione Disulfide