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

Abstract

Human lactotransferrin receptors have been recently characterized on mitogen-stimulated human lymphocytes [(1989) Eur. J. Biochem. 179, 481-487]. In order to define the lactotransferrin recognition site by these receptors, the binding to lymphocytes of several tryptic fragments, isolated from human lactotransferrin by mild tryptic hydrolysis [(1984) Biochim. Biophys. Acta 787, 90-96]; has been investigated. The 30 kDa N-tryptic fragment (residues 4-281) and the re-associated N,C-tryptic complex bind to lactotansferrin lymphocyte receptor with a dissociation constant of 44 nM and 39 nM, respectively, similar to the value obtained for the native lactotransferrin (Kd = 46 riM). However, neither the N-terminal domain II (residues 91-257) nor the 50 kDa C-tryptic fragment (residues 282-703) are recognized. These results suggest that the binding site of human lactotransferrin by the lymphocyte receptor is located in the N-terminal lobe and more precisely in the N-terminal domain I (residues 4-90 and/or 258-281).

Bovine lactoferrin region responsible for binding to bifidobacterial cell surface proteins

“…N-and C-lobes also possess unique binding regions for microbial membranes [6]. The participation of N-and C-lobes in binding to cell surface receptors has also been reported [5,7,8]. Bovine lactoferrin (bLf) C-lobe is also reported to promote the contractile activity of collagen gels more prominently than native bovine lactoferrin or it's N-lobe [9].…”

“…Each lobe has two domains (N1 and N2, C1 and C2) and can bind a single ferric ion concomitantly with one bicarbonate ion very tightly [2]. There are striking conservation between these two lobes in respect of their iron retention ability (C-lobe bind iron more tightly) [3] and biological functions (some functions of Lf are thought to be involved in the N-lobe) [4,5]. N-and C-lobes also possess unique binding regions for microbial membranes [6].…”

Lactoferrin Binds CpG-Containing Oligonucleotides and Inhibits Their Immunostimulatory Effects on Human B Cells

“…Lactoferrin binds to cells by at least two mechanisms: 1) high capacity low-affinity binding that may occur via charge-charge interactions with surface glycolipids or other molecules such as DNA (71)(72)(73)(74)(75)(76) and 2) lower capacity/higher affinity binding to one or more proteinaceous plasma membrane receptors (77)(78)(79)(80)(81)(82)(83). Lactoferrin has been reported to bind to B cells via interaction with DNA on the cell surface (74,75) and it appears that B cell binding is mediated through the highly charged N-terminal sequence of lactoferrin (84).…”

“…To our knowledge, no specific protein receptors for lactoferrin on the B cell surface have been reported. Thus, the biological response to CpG ODN bound to lactoferrin could be different in those cells possessing one or more high-affinity lactoferrin-binding mechanisms such as macrophages, hepatocytes, PHA-activated lymphocytes, and gastrointestinal epithelial cells (77)(78)(79)(80)(81)(82)(83). This requires further investigation.…”

Agglutination of Bacterial Cells ofClostridium innocuum, Bifidobacterium longum, andMicrococcus luteusby Lactoferrin and Ovotransferrin

“…These sequences have been elucidated to exist on the surface of the protein structure. 23) Rochard et al 24 ) have also reported that the binding site of Lf by the lymphocyte receptor is located at N-terminal domain I (sequence 4-90 and/or 258-281). It is interesting whether the agglutination of bacterial cells by Lf would be correlated with the corresponding sequences of these domains.…”