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Structural insights into catalysis by βC-S lyase from Streptococcus anginosus
Yuichiro Kezuka1, Yasuo Yoshida, Takamasa Nonaka
1Department of Structural Biology, School of Pharmacy, Iwate Medical University, Yahaba, Iwate, Japan.
Proteins
|June 8, 2012
Summary
Hydrogen sulfide (H2S) causes oral malodor. Researchers elucidated the H2S-producing mechanism of beta C-S lyase (Lcd) in Streptococcus anginosus using crystal structures, revealing key enzyme-substrate interactions.
Area of Science:
- Biochemistry
- Structural Biology
- Microbiology
Background:
- Hydrogen sulfide (H2S) is a key contributor to oral malodor.
- H2S production in Streptococcus anginosus is linked to the beta C-S lyase (Lcd) enzyme.
- Lcd is a pyridoxal 5'-phosphate (PLP)-dependent enzyme catalyzing sulfur-containing amino acid degradation.
Purpose of the Study:
- To elucidate the detailed H2S production mechanism of Lcd.
- To understand the structural basis of Lcd's enzymatic activity.
- To propose an improved catalytic mechanism for beta C-S lyases.
Main Methods:
- Determined crystal structures of substrate-free Lcd and reaction intermediates (external aldimine, alpha-aminoacrylate).
- Performed structural and mutational analyses of active site residues.
- Compared the mechanism with known beta C-S lyases.
Main Results:
- Enzyme structure showed minimal changes upon intermediate formation, except for the PLP-binding residue Lys234.
- Tyr60, Tyr119, and Arg365 were identified as crucial active site residues.
- Tyr119's interaction with L-serine suggests its role in L-cysteine recognition and PLP cofactor positioning.
Conclusions:
- The study provides detailed structural insights into Lcd's H2S production mechanism.
- Key residues like Tyr119 are critical for substrate binding and catalysis.
- An updated catalytic mechanism for beta C-S lyases from oral bacteria was proposed.
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