Phosphatidylinositol 3,5-bisphosphate ($\mathrm{PI}(3,5){\mathrm{P}}_2$)

phosphatidylinositol 3,5-bisphosphate is a doubly phosphorylated phosphoinositide involved in later endolysosomal organization and function. Perturbing it need not imply that initial surface uptake is defective.