Electrostatic Affinities and Binding Kinetics among $\alpha_2\textrm{I}$ Integrin Domains, Divalent Cations and 21-mer Collagen Fragment

This paper compares simulation results and experimental published data concerning the interaction between $\alpha_2\beta_1$ integrin and collagen.This phenomenon is characterized by a competition among steric, reciprocal orientation constraints of the two structures and long range electrostatic force. The published experimental results shown that the $\textrm{k}_{\textrm{on}}$ rate, for the 42-mer collagen fragment and the $\alpha_2\textrm{I}$ integrin domain complex, ranges in order of magnitude from $10^4-10^5$ M$^{-1}$s$^{-1}$. This is the lower bound of the interval defined by the diffusion limited regime and the orientational constraint. The electrostatic affinity between 21-mer collagen fragment and the $\alpha_2\textrm{I}$ integrin domain due to the divalent cations ($\textrm{Mg}^{2+}$, $\textrm{Co}^{2+}$, $\textrm{Mn}^{2+}$ and $\textrm{Ca}^{2+}$) has been expressed in terms of the Pearson correlation coefficient between the electrostatic desolvation potential of the ligand and the electrostatic interaction potential of the receptor. The obtained values of the Pearson coefficient clearly reveals the complementarity between the $\alpha_2\textrm{I}$ integrin domain and 21-mer collagen in the metal ion dependent site. Atomistic Brownian dynamics simulations applied in the diffusion limited regime, correctly reproduce the binding kinetics, of the $\alpha_2\textrm{I}$ integrin domain and the 21-mer collagen in presence of $\textrm{Mg}^{2+}$, $\textrm{Co}^{2+}$ and $\textrm{Mn}^{2+}$, according to published experimental data.