Pre-B lymphocytes, and hybridomas derived from them, synthesize immunoglobulin heavy (IgH) chain in the absence of light (L) chain. In the Abelson virus transformed line 18-81, which is representative of the pre-B cell stage, we observed that at least some of the H-chains are bound to a protein other than L-chain. Here we show that the protein (which we term immunoglobulin heavy-chain binding protein, BiP) binds non-covalently to free IgH, but not to IgH associated with IgL.

No abstract

BiP is a constitutively-expressed resident protein of the endoplasmic reticulum (ER) of all eucaryotic cells, and belongs to the highly conserved hsp70 protein family. In the ER, BiP is involved in polypeptide translocation, protein folding and presumably protein degradation as well. These functions are essential to cell viability, as has been shown for yeast. In this review, I will summarize the structural features of hsp70 proteins and focus on those experiments which revealed the biological function of BiP.

Here we show that not only transport defective but all immunoglobulin light chains interact with BiP. Association of BiP with its ligand takes place during or shortly after translation of the light chains. The biological half life of the BiP‐light chain complex depends on the fate of the light chains. Light chains which are secreted interact with BiP for only a very short time. In contrast, the complex is biologically more stable in cells which do not secrete their L chains. In these cells, dissociation from BiP correlates with the biological half life of the L chains arguing for a degradation pathway in the endoplasmic reticulum. Instead of being degraded in association with its ligand, BiP is released from the complex and binds to newly synthesized polypeptides. These results support the notion that both H and L chains require the chaperoning function of BiP before or during the process of antibody assembly.