Title : Determination of the disulfide structure and N-glycosylation
sites of the extracellular
domain of the human signal transducer
gp130
Abstract :
- gp130 is the common signal transducing receptor subunit for the interleukin-6-type family of cytokines
- Its extracellular region ( sgp130 ) is predicted to consist of five fibronectin type III-like domains and an NH2-terminal Ig-like domain
- Domains 2 and 3 constitute the cytokine-binding region defined by a set of four conserved cysteines and a WSXWS motif , respectively
- Here we determine the disulfide structure of human sgp130 by peptide mapping, in the absence and presence of reducing agent, in combination with Edman degradation and mass spectrometry
- Of the 13 cysteines present, 10 form disulfide bonds, two are present as free cysteines ( Cys(279) and Cys(469) ), and one ( Cys(397) ) is modified by S-cysteinylation
- Of the 11 potential N-glycosylation sites, Asn(21), Asn(61), Asn(109), Asn(135), Asn(205), Asn(357), Asn(361), Asn(531), and Asn(542) are glycosylated but not Asn(224) and Asn(368)
- The disulfide bonds, Cys(112)-Cys(122) and Cys(150)-Cys(160) , are consistent with known cytokine-binding region motifs
- Unlike granulocyte colony-stimulating factor receptor , the connectivities of the four cysteines in the NH2-terminal domain of gp130 ( Cys(6)-Cys(32) and Cys(26)-Cys(81) ) are consistent with known superfamily of Ig-like domains
- An eight-residue loop in domain 5 is tethered by Cys(436)-Cys(444)
- We have created a model predicting that this loop maintains Cys(469) in a reduced form, available for ligand-induced intramolecular disulfide bond formation
- Furthermore, we postulate that domain 5 may play a role in the disulfide-linked homodimerization and activation process of gp130