BiP and calreticulin form an abundant complex that is independent of endoplasmic reticulum stress

• Published in: The Plant cell Vol. 10; no. 5; pp. 813 - 823
• Main Authors: Crofts, A.J. (University of York, York, UK.), Leborgne-Castel, N, Pesca, M, Vitale, A, Denecke, J
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01.05.1998
• Subjects: Antibodies; Antiserum; ATP; BINDING; BINDING PROTEINS; CHELATEUR; CHELATING AGENTS; EDTA; ENDOPLASMIC RETICULUM; ENDOPLASMIC RETICULUM SIGNAL PEPTIDE; ESTABILIDAD; Gels; GLICOPROTEINAS; GLOBULINAS; GLOBULINE; GLOBULINS; GLYCOPROTEINE; GLYCOPROTEINS; Immunoprecipitation; INTERACTIONS; Molecular weight; Molecules; NICOTIANA TABACUM; PHASEOLIN; Plant cells; PLANT PROTEINS; PROTEINAS; PROTEINAS AGLUTINANTES; PROTEINE; PROTEINE DE LIAISON; PROTEINS; PROTOPLASTE; PROTOPLASTOS; PROTOPLASTS; QUELATOS; RETICULO ENDOPLASMATICO; RETICULUM ENDOPLASMIQUE; SIGNAL PEPTIDE; STABILITE; STABILITY
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.10.5.813

BiP is found in association with calreticulin, both in the presence and absence of endoplasmic reticulum stress. Although the BiP-calreticulin complex can be disrupted by ATP, several properties suggest that the calreticulin associated with BiP is neither unfolded nor partially or improperly folded. (1) The complex is stable in vivo and does not dissociate during 8 hr of chase. (2) When present in the complex, calreticulin masks epitopes at the C terminus of BiP that are not masked when BiP is bound to an assembly-defective protein. And (3) overproduction of calreticulin does not lead to the recruitment of more BiP into complexes with calreticulin. The BiP-calreticulin complex can be disrupted by low pH but not by divalent cation chelators. When the endoplasmic reticulum retention signal of BiP is removed, complex formation with calreticulin still occurs, and this explains the poor secretion of the truncated molecule. Gel filtration experiments showed that BiP and calreticulin are present in distinct high molecular weight complexes in which both molecules interact with each other. The possible functions of this complex are discussed