title: Short chain polyethylene glycols unusually assist thermal unfolding of human serum albumin.
abstract: In the present study we have investigated the thermal stability of the globular transport protein human serum albumin (HSA), in the presence of two small chain polyethylene glycols (namely PEG 200 and PEG 400). Both near- and far-UV circular dichroism (CD) study reveal that addition of PEG moderately increases the α-helical content of the protein without abruptly changing its tertiary structure. The hydration structure at the protein surface experiences a notable change at 30% PEG (v/v) concentration as evidenced from compressibility and dynamic light scattering (DLS) measurements. Thermal denaturation of HSA in the presence of PEG has been studied by CD and fluorescence spectroscopy using the intrinsic fluorophore tryptophan and it has been found that addition of PEG makes the protein more prone towards unfolding, which is in contrary to what has been observed in case of larger molecular weight polymers. The energetics of the thermal unfolding process has been obtained using differential scanning calorimetry (DSC) measurements. Our study concludes that both the indirect excluded volume principle as well as interaction of the polymer at the protein surface is responsible for the observed change of the unfolding process.
authors.affiliation: Department of Chemical Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India.
authors.forename: Nirnay
authors.initials: N
authors.lastname: Samanta
authors.affiliation: Department of Chemical Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India.
authors.forename: Debasish Das
authors.initials: DD
authors.lastname: Mahanta
authors.affiliation: Biophysical Chemistry Laboratory, Chemistry Division, CSIR - Indian Institute of Chemical Biology, 4, Raja S.C. Mullick Road, Kolkata 700032, India.
authors.forename: Soumitra
authors.initials: S
authors.lastname: Hazra
authors.affiliation: Biophysical Chemistry Laboratory, Chemistry Division, CSIR - Indian Institute of Chemical Biology, 4, Raja S.C. Mullick Road, Kolkata 700032, India. Electronic address: gskumar@iicb.res.in.
authors.forename: Gopinatha Suresh
authors.initials: GS
authors.lastname: Kumar
authors.affiliation: Department of Chemical Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India. Electronic address: rajib@bose.res.in.
authors.forename: Rajib Kumar
authors.initials: RK
authors.lastname: Mitra
mesh_terms: D006801:Humans; D008958:Models, Molecular; D008970:Molecular Weight; D011092:Polyethylene Glycols / Q000737:chemistry* / Q000494:pharmacology*; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects*; D012709:Serum Albumin / Q000737:chemistry*; D013696:Temperature
chemical_list: D012709:Serum Albumin; D011092:Polyethylene Glycols
keywords: Hydrophobic effect; Osmolyte; Polyethylene glycol; Protein folding; Thermodynamics