Cooperative binding promotes demand-driven recruitment of AnxA8 to cholesterol-containing membranes

The functionality of cellular membranes is critically determined by their lipid composition. Within the endolysosomal system, cholesterol is mainly found in more peripheral compartments. In contrast, cholesterol levels are low in late endosomes/lysosomes (LEL), and the occurrence of enlarged pools of this lipid is commonly linked to endolysosomal dysfunction. Here, we show that Annexin A8 (AnxA8), a member of the annexin family of Ca2 +-dependent membrane-binding proteins, participates in the endosomal regulation of cholesterol homeostasis. Depletion of AnxA8 caused accumulation of cholesterol in LEL, and pharmacological inhibition of the LEL cholesterol export recruited AnxA8 to the cholesterol-laden LEL. Biophysical analysis revealed that cholesterol enhanced the Ca2 +-dependent affinity of AnxA8 to lipid bilayers, and induced positive cooperativity of membrane binding. Our findings identify AnxA8 as a regulator of LEL cholesterol balance and point to altered membrane binding cooperativity induced by aberrant lipid composition in the target membrane as a means to control the demand-driven recruitment of this cytosolic regulatory protein.