Oxidative Folding and Assembly with Transthyretin Are Sequential Events in the Biogenesis of Retinol Binding Protein in the Endoplasmic Reticulum

• DOI: 10.1091/mbc.e08-01-0026
• Publication Date: 2008-09-25T00:53:53Z
• Authors: Sundar Rajan Selv...; Vaibhav Bhatia; Utpal Tatu
• Keywords: Calnexin; Chaperone (clinical); Proteostasis

Retinol-binding protein (RBP) is secreted out of the cell in its ligand-bound holo-form. The apo-form RBP selectively retained within endoplasmic reticulum (ER) by a mechanism that remains unknown. Using isolated microsomal system, we have recapitulated biogenesis involving oxidative folding and assembly with transthyretin ER. In addition to dissecting pathway disulfide oxidation, analyzed association early intermediates ER-chaperones. Our results show three intramolecular disulfides present (4-160, 70-174, 120-129) smallest loop (120-129) was most critical for fold. Its absence caused aggregate into an intermolecular disulfide-linked structure. After acquisition small loop, formation one two big (4-160 or 70-174) sufficient acquire folded state. cross-linking intact microsomes sedimentation on sucrose gradients, newly synthesized associated complex chaperones consisting Grp94, BiP, PDI, calnexin. constitutively ER, independent presence substrates. dissociated from this coincident loops, whereas mutant lacking both large showed persistent association. While highlighting matrix-like characteristics ER system our provide insight mechanisms will aid understanding secretion properties.