Table 3.

Equilibrium binding constants for receptor aggregation model.

Kd (nM)	Reaction	Microrates (on; nM−1s−1/off; s−1)	Manipulations
Ki	Integrin complex formation	k 2 /k 1	Kp > Ki
			increase in ligand affinity after aggregation
Kc	Filling divalent unpaired receptor	k 4 /k 3	Kc = 0.01 Ki decreased unpaired receptor Keq for binding 2nd ligand
Ka	Empty receptor pairing with bound receptor	k 6 /k 5	Ka > 0
			aggregation constant drives positive cooperativity
Kp	Population of empty paired receptors	k 10 /k 9	Kp > Ki
			increase in ligand affinity after aggregation
			Kp = 100 Kx decreased aggregate receptor Keq for binding 2nd ligand
Kx	Receptor saturation	k 8 /k 7	Kp = 100 Kx decreased aggregate receptor Keq for binding 2nd ligand

Microrate parameters are derived from published values and set to implement positive cooperativity for sequential ligand binding and receptor aggregation. The rates for integrin complex formation (K_i) are set to simulate an increase in ligand affinity post-aggregation. Populating an empty unpaired receptor is set with a hundredth fold decrease in K_eq for binding the second ligand. The aggregation equilibrium constant is set at ten times the equilibrium constant for initial complex formation to allow for aggregation to drive positive cooperativity. The population of empty paired receptors dictates an increase in ligand affinity after aggregation and is set to decrease aggregate receptor K_eq for binding second ligand for receptor saturation. These parameters are adapted from Wanant et al.²⁸, and applied here to simulate positive cooperativity in receptor aggregation pairing so that the model can be initialized and implemented with proteomic data to evaluate binding profiles.