The Effect of Protein Surface Charge Distribution on Protein-Polymer Complexation

Charge patches on protein surfaces have been known to play a significant role in the coacervation and complexation of proteins with one another and with polymers; however, quantifying this patchiness has remained elusive. We present a methodology for quantifying the charge patchiness of protein surfaces and measure how the patchiness of a panel of proteins—engineered to have the same charge, but different charge distributions—affects complexation with a variety of polyelectrolytes. The panel complexed most strongly with the strong polycation used, poly(1-methyl-4-vinylpyridinium iodide), with the proteins with the largest patches complexing over a broader range of polymer-protein ratios than those with smaller patches. Only weaker complexation was seen with the other polyelectrolytes screened, which may have been driven by the weak net negative charge of the mutants. However, the mutant with the largest patches was found to form soluble complexes with both of the weak polyanions tested, hyaluronic acid and poly(acrylic acid). A cutoff between 0.25 and 0.3 in the patchiness parameter was predictive for whether the mutants would complex with any of the polymers tested (particularly qP4VP).