Monitoring the Secondary Structure of Proteins by Near-Infrared Spectroscopy

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Abstract
Despite the numerous applications of near-infrared spectroscopy in the agricultural and bio-industrial sectors, the relevance of this technique to the study of the secondary structure of proteins has received little attention. The present research investigated the near-infrared spectra of 12 model proteins in the solid state by taking the corresponding mid-infrared data into account. The second-derivative spectra of myoglobin, β-lactoglobulin, and β-casein in the near-infrared region revealed characteristic absorption bands. While myoglobin presented absorption bands at 2055, 2170, 2289, and 2350 nm, β-lactoglobulin exhibited specific peaks at 2203, 2267, and 2300 nm. The second-derivative spectrum of β-casein showed a particularly intense band at 2269 nm. The results derived from a generalized canonical correlation analysis confirmed the potential of near-infrared spectroscopy to characterize the secondary structure of proteins: 2172 and 2289 nm appeared to be representative of α-helix structure; 2205, 2264, and 2313 nm were observed for β-sheet; 2265 nm characterized the unordered structure.