The Effects of Poly(ethylene glycol) on the Solution Structure of Human Serum Albumin C. Ragi 1 M. R. Sedaghat-Herati 2 A. Ahmed Ouameur 1 H. A. Tajmir-Riahi 1 1 Department of Chemistry-Biology, University of Que ´ bec at Trois-Rivie ´ res, C. P. 500, TR (Que ´ bec) Canada G9A 5H7 2 Department of Chemistry, Southwest Missouri State University, Springfield, MO 65804, USA Received 11 February 2005; revised 25 March 2005; accepted 25 March 2005 Published online 14 April 2005 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bip.20281 Abstract: Protein physical and chemical properties can be altered by polymer interaction. The pres- ence of several high affinity binding sites on human serum albumin (HSA) makes it a possible target for many organic and polymer molecules. This study was designed to examine the interaction of HSA with poly(ethylene glycol) (PEG) in aqueous solution at physiological conditions. Fourier transform infra- red, ultraviolet-visible, and CD spectroscopic methods were used to determine the polymer binding mode, the binding constant, and the effects of polymer complexation on protein secondary structure. The spectroscopic results showed that PEG is located along the polypeptide chains through H-bonding interac- tions with an overall affinity constant of K ¼ 4.12  10 5 M 1 . The protein secondary structure showed no altera- tions at low PEG concentration (0.1 mM), whereas at high polymer content (1 mM), a reduction of -helix from 59 (free HSA) to 53% and an increase of -turn from 11 (free HSA) to 22% occurred in the PEG–HSA com- plexes (infrared data). The CDSSTR program (CD data) also showed no major alterations of the protein secon- dary structure at low PEG concentrations (0.1 and 0.5 mM), while at high polymer content (1 mM), a major reduction of -helix from 69 (free HSA) to 58% and an increase of -turn from 7 (free HSA) to 18% was observed. # 2005 Wiley Periodicals, Inc. Biopolymers 78: 231–236, 2005 This article was originally published online as an accepted preprint. The ‘‘Published Online’’date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com Keywords: poly(ethylene glycol); protein; binding mode; binding constant; secondary structure; Fourier transform infrared; ultraviolet-visible; CD spectroscopy Correspondence to: H. A. Tajmir-Riahi; email: tajmirri@ uqtr.ca Biopolymers, Vol. 78, 231–236 (2005) # 2005 Wiley Periodicals, Inc. Contract grant sponsor: Natural Sciences and Engineering Research Council of Canada (NSERC) and FCAR (Que ´bec). 231