title: Thioredoxin-1 Selectively Activates Transglutaminase 2 in the Extracellular Matrix of the Small Intestine: IMPLICATIONS FOR CELIAC DISEASE.
abstract: Transglutaminase 2 (TG2) catalyzes transamidation or deamidation of its substrates and is ordinarily maintained in a catalytically inactive state in the intestine and other organs. Aberrant TG2 activity is thought to play a role in celiac disease, suggesting that a better understanding of TG2 regulation could help to elucidate the mechanistic basis of this malady. Structural and biochemical analysis has led to the hypothesis that extracellular TG2 activation involves reduction of an allosteric disulfide bond by thioredoxin-1 (TRX), but cellular and in vivo evidence for this proposal is lacking. To test the physiological relevance of this hypothesis, we first showed that macrophages exposed to pro-inflammatory stimuli released TRX in sufficient quantities to activate their extracellular pools of TG2. By using the C35S mutant of TRX, which formed a metastable mixed disulfide bond with TG2, we demonstrated that these proteins specifically recognized each other in the extracellular matrix of fibroblasts. When injected into mice and visualized with antibodies, we observed the C35S TRX mutant bound to endogenous TG2 as its principal protein partner in the small intestine. Control experiments showed no labeling of TG2 knock-out mice. Intravenous administration of recombinant TRX in wild-type mice, but not TG2 knock-out mice, led to a rapid rise in intestinal transglutaminase activity in a manner that could be inhibited by small molecules targeting TG2 or TRX. Our findings support the potential pathophysiological relevance of TRX in celiac disease and establish the Cys370-Cys371disulfide bond of TG2 as one of clearest examples of an allosteric disulfide bond in mammals.
authors.affiliation: From the Department of Chemistry, Stanford University, Stanford, California 94305.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Plugis
authors.affiliation: From the Department of Chemistry, Stanford University, Stanford, California 94305.
authors.forename: Brad A
authors.initials: BA
authors.lastname: Palanski
authors.affiliation: From the Department of Chemistry, Stanford University, Stanford, California 94305; the School of Medicine, Stanford University, Stanford, California 94305; the Medical Science Training Program, Stanford University, Stanford, California 94305.
authors.forename: Chih-Hisang
authors.initials: CH
authors.lastname: Weng
authors.affiliation: Department of Comparative Medicine, Stanford University, Stanford, California 94305.
authors.forename: Megan
authors.initials: M
authors.lastname: Albertelli
authors.affiliation: From the Department of Chemistry, Stanford University, Stanford, California 94305; Department of Chemical Engineering, Stanford University, Stanford, California 94305; Stanford ChEM-H, Stanford University, Stanford, California 94305. Electronic address: khosla@stanford.edu.
authors.forename: Chaitan
authors.initials: C
authors.lastname: Khosla
mesh_terms: D000818:Animals; D002446:Celiac Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*; D011503:Transglutaminases / Q000235:genetics / Q000378:metabolism*
chemical_list: C491203:TXN protein, human; C515559:Txn1 protein, mouse; D013879:Thioredoxins; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins
keywords: allosteric regulation; disulfide; intestine; thioredoxin; transglutaminase