Newly synthesized thyroglobulin (Tg), the major secretory glycoprotein of the thyroid gland, folds and homodimerizes in the endoplasmic reticulum (ER) before its export to the site of iodination, where it serves as the precursor for thyroid hormone synthesis. In families with defective Tg export, affected individuals suffer from a thyroidal ER storage disease characterized by a distended thyrocyte ER containing misfolded Tg, along with induced ER molecular chaperones. Inherited as an autosomal recessive trait, deficient Tg causes congenital hypothyroidism in newborns that, if untreated, results in goiter along with serious cognitive and growth defects. Recently, a similar phenotype has been observed in inbred cog͞cog mice, although the precise molecular defect has remained undefined. Here, we have isolated and cloned a full-length 8.5-kb Tg cDNA from cog͞cog mice and unaffected isogenic AKR͞J mice. Comparison of the complete sequences reveals that cog͞cog mice express a Leu-2263 3 Pro missense mutation in the acetylcholinesterase-homology domain of Tg. Heterologous expression studies in COS cells indicate that cog Tg exhibits a severe defect in exit from the ER. Site-directed mutagenesis of cog Tg to convert the single amino acid back to Leu-2263 restores normal Tg secretion. We conclude that the cog mutation in Tg is responsible for this ER storage disease that causes thyroid dyshormonogenesis.

We present the first identification of transient folding intermediates of endogenous thyroglobulin (Tg; a large homodimeric secretory glycoprotein of thyrocytes), which include mixed disulfides with endogenous oxidoreductases servicing Tg folding needs. Formation of disulfide-linked Tg adducts with endoplasmic reticulum (ER) oxidoreductases begins cotranslationally. Inhibition of ER glucosidase activity blocked formation of a subgroup of Tg adducts containing ERp57 while causing increased Tg adduct formation with protein disulfide isomerase (PDI), delayed adduct resolution, perturbed oxidative folding of Tg monomers, impaired Tg dimerization, increased Tg association with BiP/GRP78 and GRP94, activation of the unfolded protein response, increased ER-associated degradation of a subpopulation of Tg, partial Tg escape from ER quality control with increased secretion of free monomers, and decreased overall Tg secretion. These data point towards mixed disulfides with the ERp57 oxidoreductase in conjunction with calreticulin/calnexin chaperones acting as normal early Tg folding intermediates that can be "substituted" by PDI adducts only at the expense of lower folding efficiency with resultant ER stress.Membrane and secretory proteins are cotranslationally translocated in the lumen of the endoplasmic reticulum (ER), where they acquire their three-dimensional structure (including the formation and isomerization of disulfide bonds), typically culminating in oligomeric assembly. This is a complex task, both facilitated and monitored by ER folding enzymes and molecular chaperones. Glycoproteins are an important subset of exportable proteins, and those bearing Asn-linked oligosaccharides fold preferentially with the aid of calreticulin (CRT) and calnexin (CNX), both of which possess a lectin-like binding site that prefers association with monoglucosylated oligosaccharide processing intermediates (4). CRT and CNX might directly influence protein folding (32), but an additional critical function of these proteins is to bring newly synthesized exportable glycoproteins in close proximity with ERp57 (47), an oxidoreductase that works in a complex with CRT/CNX and promotes proper disulfide bond formation (21,46,54).Another molecular chaperone is BiP (GRP78), which binds to unfolded polypeptides, helps to prevent protein aggregation through noncovalent associations regulated by its ATPase domain (9), and works cooperatively with protein disulfide isomerase (PDI) to promote oxidative protein folding (36). Indeed, recently the concept of two distinct chaperone-oxidoreductase complexes, one comprising CRT/CNX/ERp57 and the other including BiP/PDI (37), has emerged. This fits well with earlier proposals of a reticular-like matrix in the ER lumen in which different chaperone systems are organized (25,51). In this view, PDI plays a role in the BiP system analogous to that of ERp57 in the CRT/CNX system. However, while the absence of the CRT contribution to the ERp57 system can be functionally compensated for by the presence of CNX, the...

The age-specific prevalence of dementia, its sex difference, and the relative prevalence of important types of dementia were studied in the elderly people in a Korean rural community. A two-stage approach was employed, involving screening and clinical assessment. The prevalence among individuals aged 65 and over was found to be 10.8%, with rates of 7.2% in men and 14.5% in women. The dementia was of the Alzheimer type in 60.0% of cases, multi-infarct dementia in 12.0%, mixed dementia of Alzheimer type and multi-infarct in 10.7%, alcoholic dementia in 8.0%, and others and unclassifiable in 9.3%. The prevalence of dementia of the Alzheimer type was significantly higher in women and rapidly increased with age in both sexes. The prevalence of multi-infarct dementia was not related to sex or age. Alcoholic dementia was identified only in men. These findings indicate that the prevalence of dementia in rural Korea is similar to that reported in Western countries and that the prevalence of dementia of the Alzheimer type in rural Korea is greater than that of multi-infarct dementia.

Secretion of thyroglobulin (Tg, a large homodimeric glycoprotein) is essential to deliver Tg to its site of iodination for thyroxine biosynthesis. An L2263P missense mutation in Tg has been proposed as the molecular defect causing congenital goitrous hypothyroidism in cog/ cog mice due to perturbed Tg homodimerization, resulting in its retention within the endoplasmic reticulum. The mutation falls within a carboxyl-terminal region of Tg with high structural similarity to the entirety of acetylcholinesterase (AChE), a secretory protein that also forms homodimers. We provide new evidence that authentic AChE and the cholinesterase-like domain of Tg share a common tertiary structure. Moreover, we find that a Tg truncation, deleted of the cholinesterase-like region (but not a comparably sized deletion of internal Tg regions), blocks Tg export. Appending to this truncation a cDNA encoding authentic AChE results in translation of a chimeric protein in which AChE is present in a native, enzymatically active (albeit latent) conformation, and this fully rescues Tg secretion. Introduction of the cog mutation inhibits AChE enzyme activity, and established denaturing mutations of AChE block secretion of the Tg. Additional studies show that the native structure of the AChE region functions as a "dimerization domain," facilitating intracellular transport of Tg to the site of thyroid hormonogenesis.