pH-dependent secondary conformation of bovine lens α-crystallin: ATR infrared spectroscopic study with second-derivative analysis

Abstract 

· Background: In order to simulate the usage of different formulations of ophthalmic solution, the protein conformational changes of lens α-crystallin in buffer solutions of different pH were investigated. · Methods: The secondary structure of bovine lens α-crystallin in different Mcllvaine buffer solutions (pH 2.2, 4.0, 6.0, 7.2 and 8.0) was determined by attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectrometry with second-derivative technique. The turbidity of α-crystallin in different buffer solutions was observed. · Results and conclusion: The results indicate that α-crystallin exists mainly in β-sheet structure at 1627–1637 cm^–1. The conformational components of α-crystallin may be closely similar in pH 7.2 buffer solution and in pH 8.0 buffer solution. Once α-crystallin dissolved in pH 6.0 and 4.0 buffer solution, the appearance of a component at 1618 or 1620 cm^–1, associated with the presence of intermolecular β-sheet structure or β-turn structure or amino acid side chains, implied the denaturation of α-crystallin, which was even more marked in pH 4.0 buffer solution. Due to the effect of dissociation and stability of α-crystallin in pH 2.2 buffer solution, the secondary structure of the intact α-crystallin was difficult to evaluate. This study demontrates that different pH can vary secondary conformational structure of α-crystallin, particularly if the pH is below 6.0. This suggests that the secondary structure of α-crystallin in buffer solution exhibits pH-dependent characteristics.