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			PubMed Journals: J Biol Chem

  Source:		PMID: 9837919


    		J Biol Chem. 1998 Dec 11;273(50):33423-8.
     
			Role of asparagine-linked oligosaccharides
			in protein folding, membrane targeting,
			and thyrotropin and autoantibody binding
			of the human thyrotropin receptor.

			Nagayama Y(1), Namba H, Yokoyama N, Yamashita
			S, Niwa M.

			Author Information
			(1) Department of Pharmacology 1,
			Nagasaki University School of Medicine,
			Nagasaki, 852-8523, Japan.
			nagayama@net.nagasaki-u.ac.jp

			The amino-terminal ectodomain of thyrotropin (TSH)
			receptor (TSHR) is heavily glycosylated with
			asparagine-linked (N-linked) oligosaccharides.
			The present studies were designed to evaluate
			how acquisition and processing of N-linked
			oligosaccharides play a role in the functional
			maturation of human TSHR. A glycosylation
			inhibitor tunicamycin, which inhibits the
			first step of N-linked glycosylation (acquisition
			of N-linked oligosaccharides), and a series
			of mutant Chinese hamster ovary (CHO)-Lec
			cells defective in the different steps of
			glycosylation processing were used. Inhibition
			of acquisition of N-linked oligosaccharides
			by tunicamycin treatment in CHO cells stably
			expressing TSHR produced nonglycosylated
			TSHR, which was totally nonfunctional. In
			contrast, all of the TSHRs synthesized in
			mutant CHO-Lec1, 2, and 8 cells (mannose-rich,
			sialic acid-deficient, and galactose-deficient
			oligosaccharides, respectively) bound TSH
			and produced cAMP in response to TSH with
			an affinity and an EC50 similar to those
			in TSHR expressed in parental CHO cells
			(CHO-TSHR; sialylated oligosaccharides).
			However, Lec1-TSHR and Lec2-TSHR were not
			efficiently expressed on the cell surface,
			whereas the expression levels of Lec8-TSHR
			and CHO-TSHR were essentially identical.
			All of the TSHRs expressed in CHO-Lec cells
			cleaved into two subunits. Finally, anti-TSHR
			autoantibodies from Graves' patients interacted
			with all of the TSHRs harboring different
			oligosaccharides to a similar extent. These
			data demonstrate that acquisition and processing
			of N-linked oligosaccharides of TSHR appear
			to be essential for correct folding in the
			endoplasmic reticulum and for cell surface
			targeting in the Golgi apparatus. We also
			show that complex type carbohydrates are
			not crucially involved in the interaction
			of TSHR with TSH and anti-TSHR autoantibodies.

			PMID: 9837919 [Indexed for MEDLINE]

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