ABSTRACT
About one-third of all cellular proteins pass through the secretory pathway and hence undergo oxidative folding in the endoplasmic reticulum (ER). Protein-disulfide isomerase (PDI) and related members of the PDI family assist in the folding of substrates by catalyzing the oxidation of two cysteines and isomerization of disulfide bonds as well as by acting as chaperones. In this study, we present the crystal structure of ERp27, a redox-inactive member of the PDI family. The structure reveals its substrate-binding cleft, which is homologous to PDI, but is able to adapt in size and hydrophobicity. Isothermal titration calorimetry experiments demonstrate that ERp27 is able to distinguish between folded and unfolded substrates, only interacting with the latter. ERp27 is up-regulated during ER stress, thus presumably allowing it to bind accumulating misfolded substrates and present them to ERp57 for catalysis.
Subject(s)
Endoplasmic Reticulum/metabolism , Molecular Chaperones/chemistry , Protein Disulfide-Isomerases/chemistry , Binding Sites , Biocatalysis , Calorimetry , Cell Line, Tumor , Crystallography, X-Ray , Disulfides/chemistry , Disulfides/metabolism , Endoplasmic Reticulum Stress , Humans , Hydrophobic and Hydrophilic Interactions , Models, Molecular , Molecular Chaperones/isolation & purification , Molecular Chaperones/metabolism , Oxidation-Reduction , Protein Binding , Protein Disulfide-Isomerases/isolation & purification , Protein Disulfide-Isomerases/metabolism , Protein Folding , Proteins/chemistry , Proteins/metabolism , ATPase Inhibitory ProteinABSTRACT
Evaluation of a pathophysiological role of the interleukin-6-type cytokine oncostatin M (OSM) for human diseases has been complicated by the fact that mouse models of diseases targeting either OSM or the OSM receptor (OSMR) complex cannot fully reflect the human situation. This is due to earlier findings that human OSM utilizes two receptor complexes, glycoprotein 130 (gp130)/leukemia inhibitory factor receptor (LIFR) (type I) and gp130/OSMR (type II), both with wide expression profiles. Murine OSM on the other hand only binds to the gp130/OSMR (type II) receptor complex with high affinity. Here, we characterize the receptor usage for rat OSM. Using different experimental approaches (knock-down of the OSMR expression by RNA interference, blocking of the LIFR by LIF-05, an antagonistic LIF variant and stably transfected Ba/F3 cells) we can clearly show that rat OSM surprisingly utilizes both, the type I and type II receptor complex, therefore mimicking the human situation. Furthermore, it displays cross-species activities and stimulates cells of human as well as murine origin. Its signaling capacities closely mimic those of human OSM in cell types of different origin in the way that strong activation of the Jak/STAT, the MAP kinase as well as the PI3K/Akt pathways can be observed. Therefore, rat disease models would allow evaluation of the relevance of OSM for human biology.
