Propylbenzmethylation at Val-1(¦Á) of HbA was carried out to stabilize the Hb tetramer. The propylbenzmethylated Hb at Val-1(¦Á) (PrB-Hb) was used as the starting material for site-specific PEGylation at Cys-93(¦Â) of Hb using maleimide PEG. Structural and functional properties, autoxidation rate and thermal stability of the resultant product (PEG-PrB-Hb) were measured.
Propylbenzmethylation at Val-1(¦Á) 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(¦Á) 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.
Propylbenzmethylation at Val-1(¦Á) showed higher ability than propylation at Val-1(¦Á) to improve the structural and functional properties and decrease the side effect of PEG-Hb.
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.