The Effects of Protein Hydrophobic Exposure on the Slope of the Line in the Δπ vs πi Plot

The Δπvs πi curve from monolayer surface pressure detection is a powerful method to characterize the membrane insertion. The Δπvs πi curve is fixed by two parameters, the πc and the slope. The intersected point ( πc ) of Δπvs πi curve with abscissa is generally used as a quantitative measure of the membrane insertion ability of a protein. In the current work we demonstrate a correlation between the variation in the slope of the Δπvs πi curve with protein hydrophobic exposure by performing monolayer experiments on three different proteins, human apolipoprotein H, trichosanthin, and mutant trichosanthin. The value of |slope| increases gradually following the degree of hydrophobic exposure. These findings suggest that the two parameters, the πc and the slope, will complement each other to interpret the lipid/protein interaction involved in membrane insertion.