Nonlocal interactions are responsible for tertiary structure formation in staphylococcal nuclease

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Dynamics

Background:

• Protein folding is a complex process crucial for biological function.
• Nonlocal interactions are hypothesized to drive rapid molecular collapse during folding.
• Understanding these interactions is key to deciphering protein structure formation.

Purpose of the Study:

• To investigate the role of nonlocal interactions in the tertiary structure formation of staphylococcal nuclease (SNase).
• To determine if the C-terminal region is essential for establishing native protein structure via nonlocal interactions.

Main Methods:

• Performed nonlocal interaction substitution mutation analysis on wild-type (WT) SNase.
• Created disulfide bond mutants (WT-SS and Delta140-149-SS) by substituting specific residues with cysteine.
• Assessed protein structure and refolding kinetics under various conditions (physiological, acidic).

Main Results:

• The oxidized form of Delta140-149-SS, lacking the C-terminal region, adopted a native-like structure, while the reduced form was denatured.
• Refolding kinetics for WT-SS mutants were similar to WT SNase, indicating rapid establishment of nonlocal interactions (<22 ms).
• Acidic conditions induced a more compact denatured structure in oxidized WT-SS compared to WT.

Conclusions:

• The C-terminal region of SNase is indispensable for forming the native structure through nonlocal interactions.
• Nonlocal contacts are established early in the folding process, facilitating subsequent secondary structure formation.
• This highlights the critical role of long-range interactions in achieving functional protein conformation.