Structural and Mutagenic Approach to Create Human Serum Albumin-Based Oxygen Carrier and Photosensitizer

SUMMARY: Human serum albumin (HSA) is a versatile protein found at high concentration in blood plasma and binds a range of insoluble endogenous and exogenous compounds. We have shown that complexation of functional molecules into HSA creates unique proteins never seen in nature. Complexing an iron-protoporphyrin IX into a genetically engineered heme pocket of recombinant HSA (rHSA) generates an artificial hemoprotein, which binds O(2) reversibly in much the same way as hemoglobin. A pair of site-specific mutations, (i) introduction of a proximal histidine at the Ile-142 position and (ii) substitution of Tyr-161 with Phe or Leu, allows the heme to bind O(2). Additional modification on the distal side of the heme pocket provides rHSA(triple mutant)-heme complexes with a variety of O(2) binding affinity. Complexing a carboxy-C(60)-fullerene (CF) into HSA generates a protein photosensitizer for photodynamic cancer therapy. Energy transfer occurs from a photoexcited triplet-state of HSA-CF (HSA-(3)CF(*)) to O(2), forming singlet oxygen ((1)O(2)). This protein does not show dark cytotoxicity, but induceds cell death under visible light irradiation.