Understanding the function of water during the gelation of globular proteins by temperature-dependent near infrared spectroscopy

Abstract

Water plays an indispensable role in the gelation of proteins, but its function still remains unclear. In this work, the variation of water species with the structural changes of globular proteins was investigated using temperature-dependent near infrared (NIR) spectroscopy. Ovalbumin (OVA) was used as a model protein, which forms a gel-like structure as the temperature increases through three phases, i.e., phase I (native), phase II (molten globule state), and phase III (gel state). The structural change and the content variation of different water species in the three phases of gelation were analyzed by two-dimensional correlation NIR spectroscopy and Gaussian fitting. A decrease in the water species with two hydrogen bonds (S2) was found and the change follows the same phases as OVA. In the first two phases, the change occurs after those of other water species but in the third phase, the change is faster than that of free water species. The result indicates that in the native and molten globule states, S2 is located in the hydration shell of OVA to maintain the stability of the protein structure, and then in the gel state, high temperature weakens the hydrogen bonding of S2 and leads to the destruction of the hydration shell, making OVA clusters form a gel structure.

Aquaphotomics—From Innovative Knowledge to Integrative Platform in Science and Technology

“…Similarly to perturbation by light, intentional perturbation by temperature is often used in aquaphotomics as it is possible to use temperature dependent NIR spectra to obtain structural and quantitative information of the aqueous systems [42,43,49,50]. For instance, temperature perturbation was employed to study structural changes of ovalbumin as a model protein in aqueous solutions [51]. Two-dimensional correlation NIR spectroscopy and Gaussian fitting were adopted to investigate the variation of different water species and the sequences of the changes in the structure of protein during gelation.…”

“…In a study of prion protein isoforms [47], aquaphotomics analysis of Mn and Cu prion isoforms in water solutions revealed that while binding of copper results in increased protein stability in water, the binding of manganese resulted in less stability—which led to fibril formation, responsible of neurodegenerative disease. The fact that the entire process of protein structural changes in aqueous systems can be monitored indirectly through the water absorbance pattern of the protein solution, was demonstrated in a study of amyloid protein—another protein involved in pathogenesis of neurodegenerative diseases [71]—as well as ovalbumin [51].…”

Temperature-dependent near-infrared spectroscopy for studying the interactions in protein aqueous solutions

“…Structural changes during protein gelation were studied by temperature-dependent NIR spectroscopy using ovalbumin (OVA) aqueous solution. 6 The spectra of OVA solution were recorded at temperatures from 30 to 90 C with a step of 5 C. Using CWT to enhance the spectral resolution of the spectra, the peaks corresponding to a-helix and b-sheet can be identified. The opposite trend of the variation in the spectral intensity gives a clear indication for the transformation from a-helix to b-sheet.…”

Molecular Functionality of Plant Proteins from Low- to High-Solid Systems with Ligand and Co-Solute

“…Upon heating, native globular molecules in aqueous solution unfold and expose the hydrophobic core facilitating polypeptide-polypeptide and polypeptide-water interactions [29]. This process is initiated by diminishing stability of hydrogen bonds in the hydration shell of the protein, which enables the rearrangement of chain segments to balance a multitude of attractive and repulsive forces [30]. At high enough concentrations, gels are formed upon cooling via disulfide, ionic, hydrophobic and hydrogen bonds [31].…”