Dissecting protein function: an efficient protocol for identifying separation-of-function mutations that encode...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Loss-of-function mutations are commonly used to study protein function, but cannot distinguish between specific functional defects and protein instability.
• Overexpression dominant-negative (ODN) phenotypes offer an alternative by identifying mutant proteins that disrupt function when overexpressed, assuming structural integrity.

Purpose of the Study:

• To evaluate the utility of ODN phenotypes as a sensitive measure of protein stability.
• To develop an efficient strategy for generating separation-of-function mutations.

Main Methods:

• Compared in vivo phenotypes of Est3 telomerase subunit mutations with in vitro secondary structure analyzed by circular-dichroism spectroscopy.
• Utilized reverse mutagenesis targeting conserved charged residues in EST3.
• Employed ODN screening to identify structurally stable, functionally defective mutant proteins.

Main Results:

• ODN screening proved more sensitive for assessing protein stability than monitoring protein levels.
• Mutating highly conserved charged residues to oppositely charged amino acids increased the likelihood of generating severely defective yet structurally stable est3 mutations.
• Demonstrated that ODN phenotypes correlate with protein structural stability.

Conclusions:

• ODN screening is a valuable tool for assessing protein stability and identifying separation-of-function mutations.
• Charge-swap mutagenesis targeting conserved charged residues, coupled with ODN screening, offers an efficient and broadly applicable strategy for generating separation-of-function mutations.