Title
Protein Polymer Conjugates: Improving the Stability of Hemoglobin with Poly(acrylic acid)
Author
Vindya Thilakarathne, Victoria A. Briand, Yuxiang Zhou, Rajeswari M. Kasi, Challa V. Kumar
Year
2011
Journal
Langmuir
Abstract
The synthesis, characterization, and evaluation of a novel polymer–protein conjugate are reported here. The covalent conjugation of high-molecular weight poly(acrylic acid) (PAA) to the lysine amino groups of met-hemoglobin (Hb) resulted in the covalent conjugation of Hb to PAA (Hb-PAA conjugate), as confirmed by dialysis and electrophoresis studies. The retention of native-like structure of Hb in Hb-PAA was established from Soret absorption, circular dichroism studies, and the redox activity of the iron center in Hb-PAA. The peroxidase-like activities of the Hb-PAA conjugate further confirmed the retention of Hb structure and biological activity. Thermal denaturation of the conjugate was investigated by differential scanning calorimetry and steam sterilization studies. The Hb-PAA conjugate indicated an improved denaturation temperature (Td) when compared to that of the unmodified Hb. One astonishing observation was that polymer conjugation significantly enhanced the Hb-PAA storage stability at room temperature. After 120 h of storage at room temperature in phosphate-buffered saline (PBS) at pH 7.4, for example, Hb-PAA retained 90% of its initial activity and unmodified Hb retained <60% of its original activity under identical conditions of buffer, pH, and temperature. Our conjugate demonstrates the key role of polymers in enhancing Hb stability via a very simple, efficient, general route. Water-swollen, lightly cross-linked, stable Hb-polymer nanogels of 100–200 nm were produced quickly and economically by this approach for a wide variety of applications.
Full Article
Instrument
J-710
Keywords
Circular dichroism, Secondary structure, Chemical stability, Polymers, Biochemistry, Materials