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Updated: Jun 4, 2026
05:51
Direct Detection of the Acetate-forming Activity of the Enzyme Acetate Kinase
Published on: December 19, 2011
Different active-site loop orientation in serine hydrolases versus acyltransferases
Yun Jiang1, Krista L Morley, Joseph D Schrag
1Department of Biochemistry, Molecular Biology and Biophysics, Biotechnology Institute, University of Minnesota, 1479 Gortner Avenue, Saint Paul, MN 55108, USA.
Chembiochem : a European Journal of Chemical Biology
|February 26, 2011
Summary
Researchers uncovered a key difference in enzyme active sites that explains how acyltransferases and hydrolases perform distinct biochemical reactions. This finding reveals how a specific loop orientation dictates whether enzymes build molecules or break them down.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Acyl transfer reactions are vital in synthesizing essential biomolecules like antibiotics and polyesters.
- Acyltransferases and hydrolases share similar protein structures and catalytic mechanisms, yet exhibit distinct reactivities.
- The molecular basis for this difference in reactivity has remained a significant challenge in biochemistry.
Purpose of the Study:
- To elucidate the molecular basis for the differing reactivity between acyltransferases and hydrolases.
- To identify structural differences in the active sites of these enzyme classes.
- To understand how these structural variations influence reaction mechanisms.
Main Methods:
- Comparative analysis of X-ray crystal structures of acyltransferases and hydrolases.
- Determination of the X-ray crystal structure of Pseudomonas fluorescens esterase with a bound sulfonate transition-state analogue.
- Structural comparison focusing on the oxyanion-loop orientation and active site water molecules.
Main Results:
- A distinct oxyanion-loop orientation was identified: esterases/lipases feature a carbonyl oxygen pointing towards the active site, while acyltransferases present a main-chain amide NH group.
- The crystal structure of esterase revealed a bridging water molecule in the transition state, interacting with both the carbonyl oxygen and the sulfonate analogue.
- This bridging water molecule's position suggests a role in activating attacking water in hydrolases but deactivating it in acyl transferases.
Conclusions:
- The orientation of the oxyanion loop is a critical determinant of enzyme function, differentiating acyltransferases from hydrolases.
- A bridging water molecule in the transition state plays a mechanistic role in controlling the reactivity of water in the active site.
- These findings resolve a long-standing mystery regarding the distinct catalytic activities of enzymes with similar folds.
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