Specificity of trypsin and chymotrypsin: loop-motion-controlled dynamic correlation as a determinant

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Trypsin and chymotrypsin are serine proteases with similar structures but different substrate specificities.
• External loops near the binding pocket critically influence enzyme specificity.
• Understanding the mechanism of loop-mediated specificity control is essential.

Purpose of the Study:

• To investigate the dynamic properties of trypsin and chymotrypsin using the Gaussian network model.
• To elucidate the role of two specific loops in controlling enzyme specificity.
• To analyze the correlation between loop motions and binding site residue dynamics.

Main Methods:

• Gaussian network model (GNM) simulations were employed to study enzyme dynamics.
• A clustering method was utilized to analyze correlated residue motions.
• Comparative analysis of dynamic signatures between trypsin and chymotrypsin was performed.

Main Results:

• Trypsin and chymotrypsin exhibit distinct dynamic signatures in the two loop regions.
• These loop dynamics are highly correlated with motions of residues within the substrate-binding pockets.
• Experimental replacement of trypsin loops with chymotrypsin's loops shifted trypsin's dynamics towards chymotrypsin-like behavior.

Conclusions:

• Cooperative motions between the two loops and substrate-binding sites are key determinants of enzyme activity and specificity.
• The study provides insights into allosteric regulation of enzyme function by distant structural elements.
• Dynamic properties of serine proteases can be modulated by altering loop structures.