Local rigidity of a protein molecule

Area of Science:

• Biophysics
• Protein Mechanics
• Structural Biology

Background:

• Protein substructure distribution influences mechanical properties.
• Atomic force microscopy (AFM) provides insights into protein mechanics.
• Previous mechanical extension experiments on bovine carbonic anhydrase II (BCAII) yielded preliminary data.

Purpose of the Study:

• To re-analyze mechanical extension data of BCAII, Q253C mutant.
• To estimate the distribution of Young's modulus (Y) within the protein.
• To correlate mechanical properties with enzymatic activity and structural integrity.

Main Methods:

• Re-analysis of previously reported force vs. extension curves from mechanical extension experiments.
• Estimation of Young's modulus (Y) distribution across different extension ranges.
• Comparison of mechanical properties between enzymatically active and inactive protein conformers.

Main Results:

• The enzymatically active type I conformer exhibited increasing Young's modulus (Y) from 40 to 220 MPa with extension (10-75 nm), indicating a rigid core.
• The enzymatically inactive type II conformer showed a near-constant Young's modulus (Y) of 55+/-15 MPa over the same extension range.
• These findings suggest the presence of a rigid core structure in the active conformer, absent in the inactive one.

Conclusions:

• The mechanical properties of bovine carbonic anhydrase II are dependent on its conformational state and enzymatic activity.
• The presence or absence of a rigid core structure correlates with enzymatic activity.
• This study reinforces the link between protein structure, mechanical properties, and function.