Cell-Penetrating Peptides\nTranslocate across the Plasma\nMembrane by Inducing Vesicle Budding and Collapse

Cell-penetrating peptides (CPPs) enter the cell by two\ndifferent\nmechanisms–endocytosis followed by endosomal escape and direct\ntranslocation at the plasma membrane. The mechanism of direct translocation\nremains unresolved. In this work, the direct translocation of nonaarginine\n(R9) and two cyclic CPPs (CPP12 and CPP17) into Jurkat cells was monitored\nby time-lapse confocal microscopy. Our results provide direct evidence\nthat all three CPPs translocate across the plasma membrane by a recently\ndiscovered vesicle budding-and-collapse (VBC) mechanism. Membrane\ntranslocation is preceded by the formation of nucleation zones. Up\nto four different types of nucleation zones and three variations of\nthe VBC mechanism were observed. The VBC mechanism reconciles the\nenigmatic and conflicting observations in the literature.