Lactotransferrin receptor of mouse small-intestinal brush border. Binding characteristics of membrane-bound and triton X-100-solubilized forms

Abstract

A specific lactotransferrin receptor was identified in the mouse small-intestinal brush-border membrane and the binding features were investigated in homologous and heterologous systems. The receptor was found to be specific for lactotransferrins isolated from milk of various species, but the affinity was higher toward the homologous ligand (Ka = 3.5 x 10(6) M-1 compared with 2.6 x 10(6) M-1 for both human and bovine lactotransferrins). However, the number of binding sites (n) was the same for the three lactotransferrins, namely 0.53 x 10(12)/micrograms of membrane protein. The binding of mouse lactotransferrin to its receptor was found to be pH-dependent, with an optimal binding at pH 5.5, and seemed unlikely to be carbohydrate-mediated. The receptor was demonstrated to be devoid of any affinity for human and mouse serotransferrins or for a 'serotransferrin-like' protein isolated from mouse milk. The receptor was solubilized with 1% Triton X-100 with good yield. The solubilized receptor was found to retain lactotransferrin-binding activity and sensitivity to pH.

Lactoferrin‐binding sites at the surface of HT29‐D4 cells

“…In addition, it must be precised that similar biphasic curves are obtaincd for the two iron-binding proteins even with a very low concentration of labeled ligand (50 pM; data not shown). The dissociation constant of the high-affinity binding sites for lactoferrin (& = 400 nM) agrees with data reported for other systems such as human blood monocytes (Kd = 430nM) [20], human alveolar macrophages (Kd = 500 nM) [16], small intestinal brush border of rabbit (Kd = 833 nM) [21] and mouse (Kd = 280nM) [22], and nonrosetting lymphocytes (& = 760 nM) [23]. Similarly, the dissociation constant of the high-affinity binding sites for transferrin (& = 9.29 nM) is similar to that found for human hepatoma cell lines ( K d = 7 nM) [17], human choriocarcinoma cell lines (& = 2.3 nM) [2], human blood brain barrier (Kd = 5.6 nM) [24] and human leukemic cell lines (Kd = 1.9 nM) [25].…”

The N‐terminal domain I of human lactotransferrin binds specifically to phytohemagglutinin‐stimulated peripheral blood human lymphocyte receptors

“…However, these glycoproteins differ in the number, the structure and the location of their glycans [9][10][11][12]. Otherwise, these transferrins bind to different cells such as reticulocytes (serotransferrin) [131, enterocytes (lactotransferrin) [14,15] and chick embryo red blood cells (ovotransferrin) [16], thus suggesting that specific transferrin receptors are present at the surface of these cells and recognize a glycan, a peculiar region of the polypeptide chain, or both.…”

Evaluation of the Bioactivity of Recombinant Human Lactoferrins Toward Murine Osteoblast-Like Cells for Bone Tissue Engineering

“…This most likely occur due to the structural similarity of the two glycoproteins. [51][52][53] With regard to transferrin and iron, the transferrin family is known to be potent regulators of iron homeostasis, 54 and Tfrc 1 is the primary target of transferrin in the iron transport system. It has been reported that low iron concentrations can lead to upregulation of this protein, 55 which may explain why Tfrc was differentially regulated by the iron unsaturated and saturated forms.…”