The affinity binding sites of pancreatic bile salt-dependent lipase in pancreatic and intestinal tissues

In previous studies, we have shown that the bile salt-dependent lipase (BSD L) associates with the Grp94 molecular chaperone, an association that appea rs to play essential roles in the folding of BSDL. More recently, combined biochemical and immunocytochemical investigations were carried out to show that the transport of BSDL occurs via an association with the Grp94 all alo ng the pancreatic secretory route (ER-Golgi-granules). The Grp94-BSDL compl ex is secreted with the pancreatic juice into the acinar lumen and reaches the duodenal lumen, where it is internalized by enterocytes. The dissociati on of the complex could take place within the endosomal compartment because BSDL continues further on its way to the basolateral membrane of the enter ocyte. To localize the affinity binding sites of pancreatic BSDL in pancrea tic and duodenal tissues, we have used an affinity-gold ultrastructural tec hnique. BSDL coupled to gold particles appears to interact with specific si tes in tissue sections. This was confirmed by another indirect morphologica l approach using biotin-labeled BSDL and streptavidin-gold complexes on tis sue sections. We have shown that BSDL associates with sites in the pancreat ic secretory pathway compartments and in the microvilli, the endosomal comp artment, and the basolateral membrane of enterocytes. By biochemical approa ches, biotin-labeled BSDL displayed affinities with proteins of 180-190 kD in both pancreatic and duodenal tissues. We have also shown that the Grp94- BSDL complexes, which are insensitive to denaturing conditions, are present in pancreatic homogenate but not in duodenal lysate. Thus, BSDL is able to bind protein complexes formed by either BSDL-Grp94 or Grp94 dimers.