title: Investigating the Structural Change in Protein Aqueous Solution Using Temperature-Dependent Near-Infrared Spectroscopy and Continuous Wavelet Transform.
abstract: The circulatory protein, human serum albumin (HSA), is widely used as a model protein for the study of protein structure. In this work, the structures of human serum albumin in aqueous solutions are studied using temperature-dependent near-infrared (NIR) spectroscopy with the aid of continuous wavelet transform (CWT). Near-infrared spectra of human serum albumin solutions with different concentrations were measured over a temperature range of 30-85 ℃. Then, continuous wavelet transform was performed on the spectra to enhance the resolution. As a result of the resolution enhancement, spectral bands around 4361, 4521, 4600 and 4260 cm-1were extracted from the overlapping low-resolution signals. The four bands can be assigned to the protein structures of α-helix, β-sheet, an intermediate state and side chains, respectively. The variations in intensity of the bands around 4361 and 4521 cm-1with temperature show that the increase of temperature leads to the loss of α-helical structure but the formation of β-sheet, and the denaturation temperature of human serum albumin is about 55 ℃. The variation of the band around 4600 cm-1indicates that the temperature-induced unfolding process of human serum albumin occurs through a stable intermediate state, and a significant change in the microenvironment of the side chains about 63 ℃ is observed from the variation of the band around 4260 cm-1. On the other hand, the transformed spectra in the region of 8000-5600 cm-1provide an explicit evidence for the structural changes of water during the process of protein denaturation, and the unfolding process of HSA can be reflected by these changes.
authors.affiliation: 1 Research Center for Analytical Sciences, Nankai University, China.
authors.forename: Mengli
authors.initials: M
authors.lastname: Fan
authors.affiliation: 1 Research Center for Analytical Sciences, Nankai University, China.
authors.forename: Wensheng
authors.initials: W
authors.lastname: Cai
authors.affiliation: 1 Research Center for Analytical Sciences, Nankai University, China.|2 Tianjin Key Laboratory of Biosensing and Molecular Recognition, China.|3 State Key Laboratory of Medicinal Chemical Biology, China.|4 Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), China.|5 College of Chemistry and Environmental Science, Kashgar University, China.
authors.forename: Xueguang
authors.initials: X
authors.lastname: Shao
mesh_terms: D006801:Humans; D008956:Models, Chemical; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D000075462:Serum Albumin, Human / Q000737:chemistry / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013696:Temperature; D014867:Water / Q000737:chemistry; D058067:Wavelet Analysis
chemical_list: D011506:Proteins; D014867:Water; D000075462:Serum Albumin, Human
keywords: Continuous wavelet transform; denaturation; near-infrared spectroscopy; protein structures; temperature