Effect of free L-cysteine on the structure and function of α-chymotrypsin

• Published in: Journal of molecular liquids 2019-04, Vol.280, p.79-86
• Main Authors: Asgharzadeh, Sanaz, Shareghi, Behzad, Farhadian, Sadegh, Tirgir, Farhang
• Format: Article
• Language: English
• Subjects: Circular dichroism; Fluorescence quenching; L-cysteine; Molecular dynamic simulation; α-Chymotrypsin
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2019.01.144

L-cysteine (L-Cys) is one of 20 α-amino acids, which is connected by peptide and disulfide bonds in proteins and polypeptides. The L-Cys plays a very considerable role in stabilization of protein structure at a higher level due to disulfide bridges. The interaction of small chemical molecules to proteins has been much studied in recent years. Distinguishing the thermodynamic and kinetic properties of α-chymotrypsin (α-Chy) helps us in understanding this protein. Spectroscopic and computational approaches were applied to investigate the effect of L-Cys on the structure and the activity of the α-Chy. The UV–Vis results are revealed that the most absorption peaks were found at 260–300 nm due to Trp residues. Hyperchromism shift was seen in the presence of this ligand. This was because of the forming of the ground state complex between α-Chy and L-Cys. Static quenching was seen by emission intensity changes. The more polar environment for Trp residue was recommended by the fluorescence quenching. The secondary structure alterations were slight. A reduction in the content of β-sheet structure and an increase in the a-helix were shown. Kinetic parameters display that L-Cys inhibited the activity of the enzyme by the mixed mode. Molecular docking results show a negative value for the Gibbs free energy of the binding of L-Cys to α-Chy with hydrophobic interactions. The molecular dynamic simulation revealed α-Chy becomes more stable in the presence of L-Cys. [Display omitted] •The inhibitory effect of L-Cysteine on α-Chy•The stabilization effect of L-Cysteine on α-Chy structure•The fluorescence spectroscopy and the CD studied for the interaction of L-Cysteine and α-Chy•Molecular docking and MD simulation studies on the interaction of L-Cysteine and α-Chy