Structure-Function Study Of Porins

Single channel current-voltage (IV) relations were measured from proteins that form channels across the outer membranes of Gram-negative bacteria – porins and their mutants in solutions of KCl. The wild-type porins and some of their specific mutants have known x-rays structures, which lays the foundation for this theoretical work. The ionic strength of KCl ranges from 100mM to 3M. Using the already published electrodiffusion permeation theory [1]—[3], the measured IV relations were analyzed by the Poisson-Nernst-Planck (PNP) formulation. The parameters of the permeation property in the theory are obtained by the least-squares fit to the experimental data and compared to the known structure changes in the wild-type porins and their mutants. The comparison shows that the PNP theory can successfully recover the charge difference between the wild-type and mutants; hence, the theory begins to establish the structure-function relation biological charge transport systems and other macro-molecules.