Structure and putative function of a murine epididymal retinoic acid binding protein (mE-RABP)

Vitamin A is required to maintain the epididymal epithelium. in this report , the characterization and putative functions of a murine epididymal retino ic acid-binding protein (mE-RABP) that is secreted into the lumen from the mid-/distal caput epididymidis are discussed. The amino acid sequence analy sis of the mE-RABP preprotein shows that mE-RABP is the mouse orthologue of the rat epididymal secretory protein I (ESPI). These proteins belong to th e lipocalin superfamily and bind to active retinoids but not to retinol. Th erefore, we propose that mE-RABP may function as an extracellular retinoid carrier-protein involved in the paracrine regulation of epididymal function by retinoids.