Micellar structures formed by self-assembling Congo red molecules bind to proteins penetrating into functionrelated
unstable packing areas. Here, we have used Congo red - a supramolecular protein ligand to investigate how the
intramolecular structural changes that take place in antibodies following antigen binding lead to complement activation.
According to our findings, Congo red binding significantly enhances the formation of antigen-antibody complexes. As a
result, even low-affinity transiently binding antibodies can participate in immune complexes in the presence of Congo
red, although immune complexes formed by these antibodies fail to trigger the complement cascade. This indicates that
binding of antibodies to the antigen may not, by itself, fulfill the necessary conditions to generate the signal which
triggers effector activity. These findings, together with the results of molecular dynamics simulation studies, enable us to
conclude that, apart from the necessary assembling of antibodies, intramolecular structural changes generated by
strains which associate high- affinity bivalent antibody fitting to antigen determinants are also required to cross the
complement activation threshold.
Keywords: C1q binding, complement activation, Congo red, immune complexation, supramolecular protein ligand.
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