Journal: Acta Crystallogr D Biol Crystallogr / Year: 2015 Title: Structure and catalytic mechanism of the evolutionarily unique bacterial chalcone isomerase. Authors: Maren Thomsen / Anne Tuukkanen / Jonathan Dickerhoff / Gottfried J Palm / Hanna Kratzat / Dmitri I Svergun / Klaus Weisz / Uwe T Bornscheuer / Winfried Hinrichs / Abstract: Flavonoids represent a large class of secondary metabolites produced by plants. These polyphenolic compounds are well known for their antioxidative abilities, are antimicrobial phytoalexins ...Flavonoids represent a large class of secondary metabolites produced by plants. These polyphenolic compounds are well known for their antioxidative abilities, are antimicrobial phytoalexins responsible for flower pigmentation to attract pollinators and, in addition to other properties, are also specific bacterial regulators governing the expression of Rhizobium genes involved in root nodulation (Firmin et al., 1986). The bacterial chalcone isomerase (CHI) from Eubacterium ramulus catalyses the first step in a flavanone-degradation pathway by ring opening of (2S)-naringenin to form naringenin chalcone. The structural biology and enzymology of plant CHIs have been well documented, whereas the existence of bacterial CHIs has only recently been elucidated. This first determination of the structure of a bacterial CHI provides detailed structural insights into the key step of the flavonoid-degradation pathway. The active site could be confirmed by co-crystallization with the substrate (2S)-naringenin. The stereochemistry of the proposed mechanism of the isomerase reaction was verified by specific (1)H/(2)H isotope exchange observed by (1)H NMR experiments and was further supported by mutagenesis studies. The active site is shielded by a flexible lid, the varying structure of which could be modelled in different states of the catalytic cycle using small-angle X-ray scattering data together with the crystallographic structures. Comparison of bacterial CHI with the plant enzyme from Medicago sativa reveals that they have unrelated folds, suggesting that the enzyme activity evolved convergently from different ancestor proteins. Despite the lack of any functional relationship, the tertiary structure of the bacterial CHI shows similarities to the ferredoxin-like fold of a chlorite dismutase and the stress-related protein SP1.
Contact author
Anne Tuukkanen (EMBL-Hamburg, European Molecular Biology Laboratory (EMBL) - Hamburg outstation, Notkestraße 85, Geb. 25A, 22607 Hamburg, Deutschland, Germany)
Instrument name: PETRA III EMBL P12 / City: Hamburg / 国: Germany / Type of source: X-ray synchrotron / Wavelength: 0.124 Å / Dist. spec. to detc.: 3.1 mm
Detector
Name: Pilatus 2M
Scan
Title: Subtrate-free CHI / Measurement date: Sep 23, 2013 / Storage temperature: 10 °C / Cell temperature: 10 °C / Exposure time: 0.05 sec. / Number of frames: 20 / Unit: 1/nm /
Min
Max
Q
0.0754
4.4578
Distance distribution function P(R)
Sofotware P(R): GNOM 5.0 / Number of points: 893 /
Min
Max
Q
0.235867
2.58224
P(R) point
1
893
R
0
13
Result
Type of curve: extrapolated / Standard: BSA
Experimental
Standard
Porod
MW
190 kDa
190 kDa
190 kDa
Volume
-
-
320 nm3
P(R)
Guinier
Forward scattering, I0
25450
32346.5
Radius of gyration, Rg
3.7 nm
3.97 nm
Min
Max
Error
D
-
13
0.5
Guinier point
1
73
-
+
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