Intracellular iron levels affect cell division and cell existence; hence the
viability of a cell is dependent on the presence of iron. In vertebrates, transferrin
is responsible for the transport of iron, helping to control the available iron levels
for conservation and bacteriostatic effect, and protecting cells against the toxic
effects of free iron. Uptake of iron in cells occurs predominantly by the receptormediated
endocytosis of diferric transferrin bound to the transferrin receptor on
the cell surface. To date, limited information is available as to the nature of the
interaction of transferrin with the transferrin receptor.
High affinity monoclonal antibodies are useful as probes to determine
regions of transferrin involved in binding to the transferrin receptor. For example,
monoclonal antibodies raised against the N-lobe and C-lobe of chicken
ovotransferrin have been used to demonstrate that both lobes of ovotransferrin
must be present and associated for the binding to the ovotransferrin receptor to
occur. As well, different affinities of the monoclonal antibodies to apoovotransferrin
and holo-ovotansferrin have been used as evidence that local
structural changes occur upon iron binding.
Monoclonal antibodies against human serum transferrin have been raised
and characterized. Some but not all of such antibodies inhibit the binding of
serum transferrin to its receptor. In this study, the objective was to determine the
antigenic epitope on human serum transferrin recognized by a monoclonal
antibody that inhibits the binding of transferrin to its receptor.
A bacterial cell culture system was used for the expression of N-lobe, Clobe
and C-lobe fragments of human serum transferrin as a fusion protein with
glutathione S-transferase. Using this expression system, the epitope of the antitransferrin
antibody to C-lobe, designated as F-11, was identified to a small
region on human serum transferrin. Comparison of the F-11 epitope with the
known three-dimensional structure of human serum transferrin facilitated theMedicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat
