Two domains of rat galectin-4 bind to distinct structures of the intercellular borders of colorectal epithelia

Galectin-4 (C4) is a member of a family of soluble galactoside-binding lect ins found in Various mammalian tissues. To determine the function of this p rotein in colorectal tissue, we separately produced the N- and C-terminal c arbohydrate binding domains (CBD) of rat G4 as a recombinant glutathione S- transferase (GST) fusion protein (G4-N and G4-C) and examined the tissue bi nding site(s) of each CBD by light and electron microscopy (LM and EM). At the LM level, both fusion proteins stained the intercellular borders of the surface-lining epithelial cells of colorectal mucosa. At the EM level, two proteins recognized spatially close but distinct subcellular structures. G 4-N stained electron-lucent flocculent substances freely located in the int ercellular spaces, whereas G4-C bound to the lateral cell membranes demarca ting the intercellular spaces. These findings suggest that colorectal C4 ma y be involved in crosslinking the lateral cell membranes of the surface-lin ing epithelial cells, thereby reinforcing epithelial integrity against mech anical stress exerted by the bowel lumen.