The Journal of Cell Biology, Vol 101, 652-659, Copyright © 1985 by The Rockefeller University Press
Interaction energies in lectin-induced erythrocyte aggregation
LA Sung, EA Kabat and S Chien
Two N-acetylgalactosamine-reactive lectins, Helix pomatia (HPA) and
Dolichos biflorus (DBA), were used to study the energies involved in
cell-cell interactions through the specific binding of these lectins to
their membrane receptors on genotype AO human erythrocytes (red blood
cells) (RBCs). The energy required to dissociate a unit of aggregated
membrane area (gamma d) of two RBCs bridged by lectin molecules was
determined from the shear force needed to dissociate two-cell aggregates in
a flow channel. When HPA were used as bridging molecules, gamma d (0.4 X
10(-4) to 3.8 X 10(-4) dyn/cm) was proportional to the density (D = 175 to
1,060 molecules/micron 2) of HPA molecules bound on the RBC membrane. A
similar gamma d/D ratio was also obtained for DBA. These results indicate
that the number of lectin molecules bound on the interface plays an
important role in determining the energy required for cell-cell
dissociation. The aggregation energy per unit membrane area (gamma a) in
lectin-induced aggregates was calculated from the degree of encapsulation
of a lectin-bound, heat-sphered human RBC by a normal discoid RBC. A
minimum of approximately 1,800 HPA molecules/micron 2 on the spheres was
required to form stable aggregates with the RBC. By using spheres having a
surface HPA density of 1,830 to 2,540 molecules/micron 2, or 1.1-1.5 X
10(12) combining sites/cm2, the gamma a value for HPA-induced aggregation
was found to be 2.2 X 10(-3) dyn/cm. This higher value of gamma a than
gamma d has been explained on the basis of several differences in
aggregation and disaggregation processes. The gamma a value for DBA-induced
aggregation was not obtainable by the sphere encapsulation method because
of the relative low D values. A comparison of the present results with the
published value of the free energy change of 5 kcal/mol for the
interactions of HPA and DBA with their ligands suggests that only a small
fraction of the lectin molecules bound to RBC surface participate in the
bridging of adjacent cells.
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