Propylbenzmethylation at Val-1(α) markedly increases the tetramer stability of the PEGylated hemoglobin: A comparison with propylation at Val-1(α)

Background: Hemoglobin (Hb)-based oxygen carriers (HBOCs) are potential pharmaceutical agents that can be used in surgery or emergency medicine. PEGylation can modulate the vasoactivity of Hb and is a widely used approach to develop HBOCs. However, PEGylation can significantly enhance the tetramer-dimer dissociation of Hb, which may perturb the structure of Hb and increase its observed adverse effect. Thus, it is necessary to increase the tetramer stability of the PEGylated Hb. Methods: Propylbenzmethylation at Val-1(alpha) of HbA was carried out to stabilize the Hb tetramer. The propylbenzmethylated Hb at Val-1(alpha) (PrB-Hb) was used as the starting material for site-specific PEGylation at Cys-93(beta) of Hb using maleimide PEG. Structural and functional properties, autoxidation rate and thermal stability of the resultant product (PEG-PrB-Hb) were measured. Results: Propylbenzmethylation at Val-1(alpha) led to 25-fold and 24-fold decreases in the tetramer-dimer dissociation constant of HbA and PEG-Hb, respectively. The increased tetramer stability is due to the enhanced hydrophobicity of the area around Val-1(alpha) and the increased polar interaction of Hb upon propylbenzmethylation. Thus, the structural and functional properties of PEG-Hb were improved, and its autoxidation rate and thermal denaturation were decreased. Conclusion: Propylbenzmethylation at Val-1(alpha) showed higher ability than propylation at Val-1(alpha) to improve the structural and functional properties and decrease the side effect of PEG-Hb. General significance: Our study can facilitate the biotechnological development of stable PEGylated Hb as more advanced HBOC Our study is also expected to improve the stability of the tetrameric or dimeric proteins (e.g., uric oxidase) by propylbenzmethylation at their N-terminus. (C) 2012 Elsevier B.V. All rights reserved.