J. Biol. Chem., Vol. 258, Issue 15, 9203-9207, 08, 1983
A comparison of the cell-binding characteristics of the mitogenic and nonmitogenic lectins from lima beans
ER Pandolfino, AE Namen, GR Munske and JA Magnuson
Using the two lectins from lima bean, we have tested the model for
mitogenic stimulation of lymphocytes proposed by Prujansky et al.
(Prujansky, A., Ravid, A., and Sharon, N. (1978) Biochim. Biophys. Acta
508, 137-146). The lectins used, a tetramer with two saccharide-binding
sites and an octamer with four binding sites, are specific for N-acetyl-
D-galactosamine. Our results show that cooperative binding may not be a
prerequisite for mitogenicity of all lectins. We found that neither the
weakly mitogenic tetramer nor the potently mitogenic octamer bound
cooperatively to bovine lymphocytes. The strong mitogen bound with a higher
affinity than the weak mitogen and fewer mitogen molecules bound to the
lymphocyte surface at saturation. Competitive binding experiments indicated
that both lectins bound to the same receptors. Our results suggest that the
mitogenic lectin is able to bind and cross- link more membrane receptors.
We have also studied the binding of the lima bean lectins to human red
blood cells of types A, AB, B, and O. Both lectins bound cooperatively to
type A and type AB cells and our data indicate that the lima bean lectins
bind predominantly to the type A determinant.