Bile acids as modulators of enzyme activity and stability

Area of Science:

• Biochemistry
• Enzymology
• Gastroenterology

Background:

• Bile acids are known to interact with enzymes in the digestive system.
• Prolyl endopeptidases (PEPs) are being explored for celiac sprue therapy but can be deactivated by bile acids.
• Pancreatic enzymes like trypsin and chymotrypsin are not deactivated by bile acids and can even be activated.

Purpose of the Study:

• To investigate the mechanism behind bile acid's differential effect on prolyl endopeptidases versus pancreatic enzymes.
• To understand how bile acids impact enzyme kinetics and thermodynamic stability.

Main Methods:

• Examined the effect of bile acids on the kinetics of small substrate cleavage by PEPs, trypsin, and chymotrypsin.
• Determined the effect of bile acids on the thermodynamic stabilities of these enzymes using techniques like.
• Assessed enzyme activity in the presence of physiological bile acid concentrations.

Main Results:

• Cholic acid significantly decreased the thermodynamic stability of Flavobacterium meningosepticum PEP.
• Thermostability of trypsin and chymotrypsin remained unchanged in the presence of cholic acid.
• Bile acid-mediated protein destabilization explains both PEP deactivation and trypsin/chymotrypsin activation, but specific local interactions likely account for the extent of PEP activity loss.

Conclusions:

• Bile acids act as destabilizing agents for PEPs, leading to deactivation.
• The observed effects of bile acids on enzyme activity can be explained by a common mechanism of protein destabilization.
• Specific local interactions, rather than global thermodynamic destabilization alone, are likely responsible for the significant decrease in PEP activity.