Fig. 4.

We changed the number of ligands in the extracellular region and the number of receptors on the surface below to illustrate the effect of concentration and stoichiometry on receptor oligomerization. TNF ligands are in their trimeric state. Simulations were carried out for all combinations of ligand concentrations and surface densities of receptors. At the end of each simulation trajectory, we calculated and plot the histograms for the distributions of (a) the number of ligand-receptor trans-interactions, (b) the number of receptor-receptor cis-interactions, (c) the largest oligomer found in the system, and (d) the average size of formed oligomers, respectively. Given the same number of trimeric ligands (150), we found that the number of cis-interactions keeps increasing with the increasing density of receptors. In (e), we plot the configuration with low surface densities of receptors (450). In (f), we plot the configuration with high surface densities of receptors (750). (g) Moreover, we plot the configuration with a relative low ligand concentration (450 receptors, 75 ligands). (h) In comparison, we also plot the configuration with a relative high ligand concentration (750 receptors, 1200 ligands).