pH-induced Conversion of the Transport Lectin ERGIC-53 Triggers Glycoprotein Release

• Published in: The Journal of biological chemistry Vol. 279; no. 13; pp. 12943 - 12950
• Main Authors: Appenzeller-Herzog, Christian, Roche, Annie-Claude, Nufer, Oliver, Hauri, Hans-Peter
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26.03.2004; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Biological Transport; Calcium - chemistry; Calcium - pharmacology; Carbohydrates - chemistry; Chloroquine - pharmacology; COS Cells; Cross-Linking Reagents - pharmacology; DNA - chemistry; Dose-Response Relationship, Drug; Endoplasmic Reticulum - metabolism; Glycoproteins - chemistry; Glycoside Hydrolases - metabolism; Histidine - chemistry; Humans; Hydrogen-Ion Concentration; Lectins - chemistry; Mannose - chemistry; Mannose-Binding Lectins - chemistry; Membrane Proteins - chemistry; Microscopy, Fluorescence; Models, Biological; Models, Molecular; Molecular Sequence Data; Precipitin Tests; Protein Binding; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Time Factors; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M313245200

The recycling mannose lectin ERGIC-53 operates as a transport receptor by mediating efficient endoplasmic reticulum (ER) export of some secretory glycoproteins. Binding of cargo to ERGIC-53 in the ER requires Ca2+. Cargo release occurs in the ERGIC, but the molecular mechanism is unknown. Here we report efficient binding of purified ERGIC-53 to immobilized mannose at pH 7.4, the pH of the ER, but not at slightly lower pH. pH sensitivity of the lectin was more prominent when Ca2+ concentrations were low. A conserved histidine in the center of the carbohydrate recognition domain was required for lectin activity suggesting it may serve as a molecular pH/Ca2+ sensor. Acidification of cells inhibited the association of ERGIC-53 with the known cargo cathepsin Z-related protein and dissociation of this glycoprotein in the ERGIC was impaired by organelle neutralization that did not impair the transport of a control protein. The results elucidate the molecular mechanism underlying reversible lectin/cargo interaction and establish the ERGIC as the earliest low pH site of the secretory pathway.