Essential Residues, W 177 and R 198, of LukF for Phosphatidylcholine-Binding and Pore-Formation by Staphylococcal γ-Hemolysin on Human Erythrocyte Membranes

Abstract

LukF and Hlg 2 of staphylococcal γ-hemolysin assemble into hetero-oligomeric pores on human red blood cells (HRBC). Here, we demonstrate, using a single-molecule imaging technique, that a W 177 T/R 198 T mutant of LukF, which exhibits no binding activity toward phosphatidylcholine, could form intermediate oligomers with Hlg 2, including dimers, tetramers, and hexamer/heptamers, on HRBC. But, the mutant neither caused K⁺ efflux nor lysed HRBC, indicating that functional pores were not formed. Hence, we conclude that the W 177 and R 198 residues are essential for proper pore-formation by staphylococcal γ-hemolysin. We also suggest that the interaction between the W 177 and R 198 residues, and phosphatidylcholine on membranes is the key to the formation of functional pores.