Figure 7.

Schematic of the intermediates in H₂L₂ Ig assembly and role of BiP in the process. Although BiP can associate transiently with other Ig heavy chain domains, the C_H1 domain is the primary site of BiP binding that is responsible for the retention of unassembled heavy chains. Unlike the other heavy chain domains, the C_H1 domain remains unfolded and unoxidized in the absence of LCs. Synthesis and binding of a folding competent LC to the heavy chain promotes BiP release by an undefined mechanism and allows the C_H1 domain to fold. The completely folded and assembled Ig molecule is now transport competent.