MOLECULAR CHAPERONES INVOLVED IN PROTEIN-DEGRADATION IN THE ENDOPLASMIC-RETICULUM - QUANTITATIVE INTERACTION OF THE HEAT-SHOCK COGNATE PROTEIN BIP WITH PARTIALLY FOLDED IMMUNOGLOBULIN LIGHT-CHAINS THAT ARE DEGRADED IN THE ENDOPLASMIC-RETICULUM

In the absence of immunoglobulin heavy-chain expression, some immunogl obulin light (L) chains are retained and degraded within the cell. We investigated the fate of two different nonsecreted murine L chains whi ch exhibit different half-lives (50 min and 3-4 hr), Our results demon strate that both nonsecreted L chains are quantitatively bound to BiP as partially oxidized molecules. The kinetics of L-chain degradation c oincided with those of L-chain dissociation from BiP, which suggests t hat these two processes are functionally related. L-chain degradation does not depend on vesicular transport, indicating that these soluble proteins are degraded in the endoplasmic reticulum (ER). In contrast, secreted L chains, which interact only transiently with BiP, are compl etely oxidized and are not degraded even when they are artificially re tained in the ER, Our data support the model that, by means of BiP int eraction, the ER degradation mechanism has the potential to discrimina te between partially and completely folded molecules.