title: Fourier transform IR attenuated total reflectance spectroscopy studies of cysteine-induced changes in secondary conformations of bovine serum albumin after UV-B irradiation.
abstract: Fourier transform IR spectroscopy equipped with attenuated total reflection was used to investigate the cysteine-induced alteration of the protein secondary structure of bovine serum albumin (BSA) in aqueous solution before and after UV-B irradiation. Several amino acids were also studied. The results indicate the unchanged IR spectra of BSA coincubated with amino acids, except cysteine, did not change after 72-h UV-B irradiation. There was no difference in the IR spectrum of the unirradiated BSA coincubated with cysteine. A shoulder at 1620 cm(-1) attributed to the intermolecular beta-sheet structure was observed for the IR spectrum of BSA coincubated with cysteine after 72-h UV-B irradiation. Moreover, the peak intensity at 1303 cm(-1) that is due the alpha-helix structure was reduced, but the peak intensity at 1247 cm(-1) corresponding to beta-sheet structures was increased. Longer UV-B exposure for a BSA solution coincubated with cysteine changed the BSA solution from clear to viscous to gel form in which a transparent gel and another white gel were simultaneously observed. A gradual IR spectral alteration was found for BSA coincubated with cysteine and subjected to increased UV-B irradiation. The longer UV-B irradiation yielded increased intensity at 1620 cm(-1). The second-derivative IR peaks at 1655, 1631, and 1548 cm(-1) were shifted to 1650, 1620, and 1544 cm(-1), respectively, by the increase of UV-B irradiation, suggesting a progressive transformation from an alpha-helix to an intermolecular beta-sheet structure for BSA coincubated with cysteine. This strongly implies that longer UV-B exposure time for the BSA solution in the presence of cysteine did alter the protein secondary structures of BSA more, thus inducing gel formation by protein aggregation.
authors.affiliation: Biopharmaceutics Laboratory, Department of Medical Research and Education, Veterans General Hospital-Taipei, Shih-Pai, Taipei, Taiwan, Republic of China.
authors.forename: Yen-Shan
authors.initials: YS
authors.lastname: Wei
authors.forename: Shan-Yang
authors.initials: SY
authors.lastname: Lin
authors.forename: Shun-Li
authors.initials: SL
authors.lastname: Wang
authors.forename: Mei-Jane
authors.initials: MJ
authors.lastname: Li
authors.forename: Wen-Ting
authors.initials: WT
authors.lastname: Cheng
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002417:Cattle; D003545:Cysteine / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D000596:Amino Acids; D008055:Lipids; D012710:Serum Albumin, Bovine; D008239:Lysine; D003545:Cysteine