Fig. 2.

Slow LAT Y132 phosphorylation and spatial localization. (A) depicts capacity vs. number of signaling steps $C\left(N\right)$ for the T cell network presented in Fig. 1B where Y132 phosphorylation is a kinetic proofreading step: Speeding up Y132 phosphorylation via G131 mutation yields the green curve, and wild type (WT) is given by the red curve. The corresponding curves for the network shown in SI Appendix, Fig. S3A are the blue (G131 mutation) and orange (WT) curves; the Inset shows the drop in capacity due to the G131 mutation. (B) Numerical calculations of $N_{L,min}$ (minimum number of ligand-associated steps) derived from the network shown in SI Appendix, Fig. S4: For a fixed set of rate constants (SI Appendix, Table S4), $N_{L,min}$ is calculated by finding the smallest value of$N_L$(number of ligand-associated steps) that gives an error rate $\eta <{10}^{-4}$. The calculation is repeated for a range of ${\tau }_f/{\tau }_s$ (ratio of half-lives of agonist to self ligands) and two values of $L_f^T/L_s^T$ (ratio of concentrations of agonist to self ligands).