Multisite promiscuity in the processing of endogenous substrates by human carboxylesterase 1

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Human carboxylesterase 1 (hCE1) is a serine hydrolase involved in processing drugs and endobiotics.
• hCE1 plays a role in cholesterol metabolism, catalyzing reactions like cholesterol ester hydrolysis and fatty acyl ethyl ester synthesis.
• The structural basis for hCE1's ability to process large substrates remained unclear.

Purpose of the Study:

• To elucidate the structural basis for hCE1's broad substrate specificity and diverse catalytic functions.
• To investigate the role of additional ligand-binding sites beyond the active site.

Main Methods:

• Determined four crystal structures of the hCE1 glycoprotein.
• Complexed hCE1 with endogenous substrates/analogues: Coenzyme A, palmitate, cholate, and taurocholate.

Main Results:

• Revealed that hCE1 possesses two additional ligand-binding sites in addition to its active site.
• These sites exhibit non-specific ligand-binding properties, contributing to enzyme promiscuity.
• Demonstrated the structural capacity for hCE1 to perform multiple distinct catalytic events via multisite promiscuity.

Conclusions:

• hCE1 utilizes multisite promiscuity, employing multiple non-specific binding sites to perform distinct catalytic actions.
• These findings expand the understanding of enzyme promiscuity and hCE1's role in cellular metabolism.