FTIR study on heat-induced and pressure-assisted cold-induced changes in structure of bovine ?-lactalbumin: Stabilizing role of calcium ion

Abstract

The second derivative FTIR study of heat‐induced and pressure‐assisted cold‐induced changes in the secondary structure of bovine α‐lactalbumin was carried out for native holoprotein and calcium ion depleted apoprotein. The secondary structure and compactness of α‐lactalbumin were examined in a temperature range from 20 to 80°C during the heat treatment and 20 to −15°C during the pressure‐assisted cold treatment. This was the first FTIR study on the pressure‐assisted cold denaturation of a protein. Because protein solutions had close to neutral pD and low ionic strength, the apoprotein remained in the molten globule state and the holoform maintained its native tertiary structure. In order to distinguish between unfolding‐related and partially deuterated exchange‐related spectral changes, we examined both the fully deuterated holoform and the partially deuterated holoform. The quantitative analysis of the spectral changes in the amide I/I′ vibrational band revealed that the 3(10) helices were more prone to thermal unfolding than the α helices. We observed that the protein's compactness and secondary structure were both considerably stabilized against an increase and decrease in temperature by the presence of a calcium ion. Under the conditions of this study, only the apoprotein was susceptible to the cold denaturation. In contrast to this, an unexpected linear increase of the α‐helical content was observed upon the cooling of the holoprotein under high pressure. The results were discussed in reference to the existing crystallographic data for crystals of human α‐lactalbumin grown at two different temperatures. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 29–39, 2001

Effects of the Low-Temperature Transitions of Confined Water on the Structures of Isolated and Cytoplasmic Proteins

“…[31][32][33][34][35][36][37] In this method, the second derivative of the IR spectra is obtained (in the Amide I and II regions), and then the intensity of the bands is correlated to the protein secondary structure. 31,33,35,36,[38][39][40][41] In the case of the Amide II band, two peaks appear in the second derivative:…”

“…Note that as opposed to the Amide I band the Amide II band does not include spectral contributions from water and therefore is more suitable for structural analysis. Second derivative analysis is a standard procedure utilized to quantify the secondary structure of proteins. − In this method, the second derivative of the IR spectra is obtained (in the Amide I and II regions), and then the intensity of the bands is correlated to the protein secondary structure. ,,,,− In the case of the Amide II band, two peaks appear in the second derivative: (1) β-sheet band (1526−1504 cm −1 ) − and (2) α-helix + β-sheet band (1540−1560 cm −1 ). , The intensities of these bands were measured with respect to a common baseline for all the spectra.…”

Development of silver/α-lactalbumin nanocomposites: a new approach to reduce silver toxicity

“…Native ALA (Fig. 3a) showed high similarity with previously reported ALA spectra [20]. Two significant signal changes were observed in the spectrum of ALAred (Fig.…”

Effect of high-pressure treatment on the electrospray ionization mass spectrometry (ESI-MS) profiles of whey proteins

“…This difference between the two WPI products may be attributed to several factors. Firstly, and probably most importantly, Bipro s contains a reported amount of 1200 ppm calcium whereas Inpro s contains 5293 ppm calcium; since a-la binds Ca 2+ , the 4-fold higher calcium content in Inpro s by comparison with Bipro s may result in increased structural stability of a-la (Dzwolak, Kato, Shimizu, & Taniguchi, 2000). Secondly, Bipro s WPI is produced using an ionexchange resin to concentrate the liquid whey whereas Inpro s is produced by cross-flow microfiltration, and these differences in production methodologies may alter the conformation of the protein components in WPI.…”