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Structural basis for substrate specificity in human monomeric carbonyl reductases.
Ewa S Pilka1, Frank H Niesen, Wen Hwa Lee
1Structural Genomics Consortium, University of Oxford, Headington, United Kingdom.
Plos One
|October 21, 2009
Summary
Carbonyl reductase 3 (CBR3) exhibits narrower substrate specificity compared to CBR1, acting on specific xenobiotics like orthoquinones. Structural differences in active sites explain these substrate specificity variations, suggesting a minor role for CBR3 in xenobiotic metabolism.
Area of Science:
- Biochemistry
- Enzymology
- Drug Metabolism
Background:
- Carbonyl reduction is a key Phase I metabolic pathway for xenobiotics.
- Aldo-keto reductases and short-chain dehydrogenases/reductases are major enzyme families involved.
- Human carbonyl reductase 1 (CBR1) has a broad substrate spectrum, while its paralog, CBR3, is less characterized.
Purpose of the Study:
- To characterize the substrate specificity and structure-activity relationships of carbonyl reductase 3 (CBR3).
- To compare CBR3 with its paralog, carbonyl reductase 1 (CBR1).
- To elucidate the structural basis for differences in substrate specificity between CBR1 and CBR3.
Main Methods:
- Screening of a focused xenobiotic compound library against CBR3.
- Crystallization of CBR3.
- Substrate docking and site-directed mutagenesis.
- Kinetic analysis and comparison with CBR1.
Main Results:
- CBR3 demonstrated narrower substrate specificity than CBR1, acting on orthoquinones, isatin, and oracin.
- Active sites of CBR1 and CBR3 differ in shape and surface properties despite high sequence identity.
- Specific residues and loops within the active site, including Trp229/Pro230 and Ala235/Asp236, were identified as critical for substrate specificity differences.
Conclusions:
- Structural variations in the active site, particularly in substrate binding loops, dictate the substrate specificity of CBR3.
- CBR3 plays a likely minor role in overall xenobiotic metabolism compared to CBR1.
- Further characterization of CBR3 provides insights into enzyme evolution and drug metabolism.
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