| Lactoferrin (Lf), an 80 kD, single-chain glycoprotein, is abundant in human milk, binds iron tightly, and has been proposed to have many functions such as facilitating iron absorption, antimicrobial, and immunomodulating activities. Lf receptors (LfRs) have been found in several tissues including small intestine, liver, and lymphocytes, indicating that a primary biological function of Lf is mediated through these LfRs.; We here for the first time demonstrate the cloning of a UR gene from human and mouse small intestine, expression of the recombinant UR in a baculovirus-insect cell system, and its interaction with Lf. RT-PCR revealed that human UR is expressed at especially high levels in human fetal small intestine, but not as much in adult small intestine or in Caco-2 cells. The LfR is anchored to the apical membrane of Caco-2 cells by glycophosphatidyl inositol and uptake of Lf-bound 59Fe by LfR-transfected Caco-2 cells was significantly higher than that by mock-transfected cells. These results indicate that the UR on the apical membrane of human enterocytes mediates Lf-bound Fe transport. Mouse UR is expressed in early embryos, suggesting that the receptor-mediated function of Lf is important for embryonic development and that the mouse can be used to investigate biological functions of Lf in vivo. We also developed a recombinant HU (rHLf) expression system using rice and achieved a production level sufficient for commercial applications. We observed that rHLf has characteristics identical to native HU (nHLf) with regard to iron binding, antimicrobial activity, and binding/uptake to Caco-2 cells. Stability of rHLf after exposure to heat, low pH, or in-vitro digestion was also similar to nHLf, suggesting that rHLf can be used in infant foods.; In summary, we disclose genetic and biochemical information on the LfR, which is useful for studying the primary function of Lf Recombinant HLf expressed in rice is likely to act in infant small intestine in a manner similar to nHLf. Those functions include receptor-mediated mechanisms, possibly facilitating iron absorption and/or regulating the immune system, and non-receptor-mediated mechanisms such as antimicrobial activity. |
