Recombinant human Hb-SOD fusion proteins

Abstract

Hemoglobin (Hb) can produce reactive oxygen species, including superoxide anions, which are intrinsically toxic. Superoxide dismutase (SOD) is present in red blood cells (RBCs) and provides important protection against such oxidative stress. Upon hemolysis, Hb becomes released from the RBCs and the normal protection systems involving SOD and catalase become very inefficient. In these instances, both the Hb protein in itself and its cellular surroundings may be exposed to severe oxidative damage. In order to generate less toxic Hb variants, we have produced fusion proteins between SOD and HbA. The fusion protein has been prepared by coexpressing the human Hb α-chain linked to the manganese SOD gene as a chimeric construct together with the native β-chain Hb gene in Eschericia coli. The engineered SOD-Hb fusion protein retains the oxygen-binding capacity and, moreover, decreases cytotoxic ferrylHb (HbFe(4 +)) formation when exposed to superoxide radicals. The SOD-Hb fusion protein is also substantially less prone to autoxidation. Our findings not only provide insight into the synergistic functions between SOD and Hb when they are closely and spatially organized, but could also potentially be used to develop therapeutic blood substitutes with more efficient oxygen carrying capabilities.