Cross-reacting antigens of myoid cells of the human thymus and stable L-forms of group a streptococcus

Beletskaya, L. V.; Vul'fovich, Yu. V.; Gnezditskaya, É. V.; Goncharova, S. A.

doi:10.1007/bf00834366

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“…35). Lactoferrin may then act in its capacity to regulate the development and function of lymphocytes and other immune cells (1,(5)(6)(7)(8). We have not examined the urine of term or "mature" breast-fed infants for the presence of intact lactoferrin or other intact proteins of maternal origin.…”

Section: Discussionmentioning

confidence: 99%

Structurally intact (78-kDa) forms of maternal lactoferrin purified from urine of preterm infants fed human milk: identification of a trypsin-like proteolytic cleavage event in vivo that does not result in fragment dissociation.

Hutchens

Henry

Yip

1991

Proc. Natl. Acad. Sci. U.S.A.

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Two forms of lactoferrin, an intact lactoferrin and a "nicked" but apparently intact (i.e., 78-kDa) form, have been isolated from the urine of preterm infants fed human milk. These two forms of lactoferrin, demonstrated to be entirely of maternal origin, were copurified using affinity columns of immobilized single-stranded DNA-agarose. The relative concentrations of the intact lactoferrin and the "nicked" lactoferrin were determined after denaturation and separation by reverse-phase HPLC. N-terminal sequence analyses showed that the Intact 78-kDa form had lost two residues from its N terminus. The nicked 78-kDa form was composed of only two fragments; one fragment was identified as the N terminus of the N-lobe (residues 3-283). The other fragment started with Ser-284 and included the a-helical structures at the C terminus of the N-lobe, as well as the entire C-lobe. Although no disulfide bonds connect these two fragments, they were tightly associated in vivo and were not separated in vitro except under denaturing conditions. Limited in vitro digestion of human milk lactoferrin with trypsin produced a nicked, but stable (78-kDa), form of DNA-binding lactoferrin nearly indistinguishable from the isolated urinary lactoferrin, except for the absence of one additional arginine residue at the N terminus of the N-lobe. Residues involved in the stable molecular interaction between fragments were evaluated using data obtained from the high-resolution crystal structure of hololactoferrin. Two features, entirely within the N-lobe, account for the lack of fragment dissociation after cleavage at residue 283 in vivo: an extensive interface at the hinge region behind the ironbinding cleft and an "anchor" sequence traversing the remainder ofthe N-lobe at 90' relative to the fragment interface. These results document the remarkably limited degradation of absorbed lactoferrin in vivo and suggest that iron-binding activity, receptor-binding properties, and postulated immune cell regulatory functions remain intact.Lactoferrin is a 78-kDa metal-binding protein found in milk and various other mucosal secretions (1). It is also a component of neutrophil secretory granules and is generally thought to be important in host defense (1, 2). It has been associated with the promotion of cell growth (e.g., refs. 3 and 4), regulation of hematopoiesis, and immune-modulating properties (e.g., refs. 5-8) in vitro. Little, however, is known about the function and metabolism of lactoferrin in vivo.Lactoferrin is the major protein component of human colostral whey (9) and has been a focus of attention in numerous investigations of the nutrition and host defense of term and preterm infants (10-17). Since human lactoferrin has been cloned (18), overexpression and large-scale production are imminent. Thus, an increased need for the characterization of lactoferrin structure, function, and metabolism in vitro is anticipated. We have reported the identification and purification of intact (78- (20). In addition to identifying intact lactoferrin in ...

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