Which phospholipid contributes a charge of -4 at pH 7?

Phosphatidylinositol 4,5-bisphosphate is indeed the correct choice because its structure contains multiple phosphate groups that contribute to its overall negative charge. At physiological pH, which is approximately 7, the two phosphate groups on the inositol head group remain ionized, giving a total charge of -4.

In contrast, other phospholipids in the list do not carry the same degree of negative charge at pH 7. Phosphatidylcholine and phosphatidylethanolamine have neutral or near-neutral charges under these conditions due to their single phosphate group and overall charge balance with their respective head groups. Cardiolipin, while it does contain multiple phosphate groups, typically carries a -2 charge at pH 7 because it contains two glycerol phosphate units. Thus, phosphatidylinositol 4,5-bisphosphate uniquely exhibits a -4 charge at physiological pH.