Folding of human intestinal lactase-phlorizin hydrolase.

The folding of human intestinal prolactase-phlorizin hydrolase (pro-LPH) has been analyzed in a cell-free transcription/translation system. In the presence of the thiol oxidant GSSG, disulfide bond formation in pro-LPH can be promoted concomitant with the binding of the molecule to a conformation-specific monoclonal anti-LPH antibody. Under these conditions, pro-LPH does not bind to the molecular chaperone BiP. In the absence of GSSG, on the other hand, pro-LPH does not bind to the monoclonal anti-LPH antibody, but can be immunoprecipitated with a polyclonal antibody that is directed against a denatured form of the enzyme. In this case, interaction of pro-LPH with immunoglobulin heavy chain binding protein can be discerned. The results demonstrate the existence of intramolecular disulfide bonds that are essential for the promotion of pro-LPH to a native conformation. Furthermore, BiP is involved in the folding events of pro-LPH.