Modified globin proteins with altered electron transport pathway
The present invention relates to a modified porphyrin-based oxygen-carrying protein, such as haemoglobin, which has been found, in its unmodified state to have a low affinity site of electron transfer and a high affinity electron transfer between a reductant and ferryl haem iron via one or more protein amino acids. The invention provides such proteins that comprise a modification to enhance this pathway.
1. A composition for use as a human blood substitute, wherein said composition a modified porphyrin-based oxygen-carrying protein and a reductant in a physiologically acceptable carrier, said protein in an unmodified state comprising a low affinity site of electron transfer between the reductant and a ferryl haem iron,
wherein said modified protein comprises a modification to enhance or introduce a high affinity electron transfer pathway between the reductant and a ferryl haem iron via one or more amino acids,
wherein
said protein in an unmodified state is a member of the mammalian haemoglobin beta chain superfamily comprising Phe at the C7 position and the modified protein is a member of the mammalian haemoglobin beta chain superfamily, comprising a modification which is a Phe>Tyr substitution at the C7 position.
2. The composition of claim 1 wherein said protein in an unmodified state is a mammalian haemoglobin beta chain subunit comprising Phe at the C7 position and the modified protein is a mammalian haemoglobin beta chain subunit comprising a modification which is a Phe>Tyr substitution at the C7 position.
3. The composition of claim 1 wherein the modified protein is a human haemoglobin beta chain subunit or a member of the human haemoglobin beta chain superfamily.
4. The composition of claim 1 wherein the modified protein is a human beta, gamma or delta chain haemoglobin.
5. The composition of claim 1 wherein the modified protein is a human haemoglobin beta chain subunit wherein the modification is Phe41>Tyr.
6. The composition of claim 1 wherein the modified protein is present as a member of a dimer, tetramer or multimer.
7. The composition of claim 6 wherein the dimer, tetramer or multimer is cross-linked.
8. The composition of claim 1 wherein the modified protein is present in the form of a tetramer comprising two alpha globin subunits and two subunits of the modified protein.
9. The composition of claim 1 wherein the modified protein is in the form of a conjugated protein comprising the modified protein conjugated to a protecting group, wherein the protecting group is an anti-oxidant.
10. The composition of claim 1 wherein the modified protein is in the form of a conjugated protein comprising the modified protein conjugated to a protecting group, wherein the protecting group is a polyalkylene oxide.