Substantial increase of protein stability by multiple disulphide bonds

Area of Science:

• Biochemistry
• Structural Biology
• Protein Engineering

Background:

• Disulphide bonds are known to stabilize protein structures, primarily by reducing the configurational entropy of the unfolded polypeptide chain.
• Phage T4 lysozyme, a naturally disulphide-free enzyme, serves as a model system for studying the impact of engineered disulphide bonds on protein stability.

Purpose of the Study:

• To investigate the cumulative effect of multiple disulphide bonds on the stability of phage T4 lysozyme.
• To determine if the stability contributions of individual disulphide bonds are additive when combined within the same protein.

Main Methods:

• Site-directed mutagenesis was used to engineer single and multiple disulphide bonds (e.g., 3-97, 9-164, 21-142) into phage T4 lysozyme.
• Reversible thermal denaturation experiments were performed to measure the melting temperature (Tm) of wild-type and mutant lysozyme variants.

Main Results:

• Engineered single disulphide bonds in T4 lysozyme significantly increased protein stability compared to the wild-type.
• Combining two or three stabilizing disulphide bonds resulted in an approximately additive increase in melting temperature.
• The triple-disulphide variant exhibited a 23.4 degrees C higher melting temperature than the wild-type enzyme.

Conclusions:

• The stability enhancements conferred by individual disulphide bonds are largely additive.
• Combining multiple engineered disulphide bonds offers a powerful strategy for substantially improving protein stability.
• This approach has significant implications for protein engineering and the development of more robust enzymes.