  While cooperativity in ligand-induced receptor dimerization has been linked
with receptor-receptor couplings via minimal representations of physical
observables, effects arising from higher-order oligomer (e.g., trimer and
tetramer) formations of unobserved receptors have received less attention.
Here, we propose a dimerization model of ligand-induced receptors in
multivalent form representing physical observables under basis vectors of
various aggregated receptor-states. Our simulations of multivalent models not
only reject Wofsy-Goldstein parameter conditions for cooperativity, but show
higher-order oligomer formations can shift cooperativity from positive to
negative.
