Abstract
Quaternary amine of diethylaminoethyl rosin ester (QRMAE), chemically synthesized biocompatible rosin based cationic surfactant, has various biological applications including its use as a food product additive. In this study, we examined the amorphous aggregation behavior of mammalian serum albumins at pH 7.5, i.e., two units above their isoelectric points (pI ~5.5), and the roles played by positive charge and hydrophobicity of exogenously added rosin surfactant QRMAE. The study was carried out on five mammalian serum albumins, using various spectroscopic methods, dye binding assay, circular dichroism and electron microscopy. The thermodynamics of the binding of mammalian serum albumins to cationic rosin modified surfactant were established using isothermal titration calorimetry (ITC). It was observed that a suitable molar ratio of protein to QRMAE surfactant enthusiastically induces amorphous aggregate formation at a pH above two units of pI. Rosin surfactant QRMAE-albumins interactions revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions that play an important role towards the formation of hydrophobic interactions-driven amorphous aggregate. Amorphous aggregation of proteins is associated with varying diseases, from the formation of protein wine haze to the expansion of the eye lenses in cataract, during the expression and purification of recombinant proteins. This study can be used for the design of novel biomolecules or drugs with the ability to neutralize factor(s) responsible for the aggregate formation, in addition to various other industrial applications.
Highlights
In recent years, protein aggregation-related diseases have emerged as the topics of interest in the field of protein engineering
We propose how Quaternary amine of diethylaminoethyl rosin ester (QRMAE) can possibly induce the amorphous aggregation of mammalian serum albumin above two units of pI and we list the factors that trigger the formation of amorphous aggregate
The enhanced absorbance at 350 nm was observed in the protein sample which was incubated with QRMAE surfactant at pH value above two units of its pI
Summary
Human serum albumin (A1887), bovine serum albumin (A7030), porcine serum albumin (A1830), rabbit serum albumin (A0764), sheep serum albumin (A3264), thioflavin T (ThT) and 1-anilino-8-naphthalene sulfonate (ANS) were procured from Sigma Aldrich (USA), whereas sodium di-hydrogen orthophosphate, di-sodium hydrogen orthophosphate, sodium acetate and glacial acetic acid buffer components were procured from Qualigens, India. Double distilled water was used throughout the study. 697) was synthesized as described in the previous work [35, 36]. A stock solution of mammalian serum albumin was made in 20 mM sodium phosphate buffer of pH 7.5 and protein concentration was determined spectrophotometrically at 280 nm by using. E1% 1cm of (HSA), (PSA), (SSA) and M-1cm-1 (BSA) (RSA) on
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