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Updated: Jun 23, 2026
Biochemical and Structural Characterization of the Carbohydrate Transport Substrate-binding-protein SP0092
Published on: October 2, 2017
Structural and kinetic analysis of an MsrA-MsrB fusion protein from Streptococcus pneumoniae
Young Kwan Kim1, Youn Jae Shin, Won-Ho Lee
1Division of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, Korea.
Abstract:
Methionine sulphoxide reductases (Msr) catalyse the reduction of oxidized methionine to methionine. These enzymes are divided into two classes, MsrA and MsrB, according to substrate specificity. Although most MsrA and MsrB exist as separate enzymes, in some bacteria these two enzymes are fused to form a single polypeptide (MsrAB). Here, we report the first crystal structure of MsrAB from Streptococcus pneumoniae (SpMsrAB) at 2.4 A resolution. SpMsrAB consists of an N-terminal MsrA domain, a C-terminal MsrB domain and a linker. The linker is composed of 13 residues and contains one 3(10)-helix and several hydrogen bonds interacting with both MsrA and MsrB domains. Interestingly, our structure includes the MsrB domain complexed with an SHMAEI hexa-peptide that is the N-terminal region of neighbouring MsrA domain. A kinetic analysis showed that the apparent K(m) of SpMsrAB for the R-form-substrate was 20-fold lower than that for the S-form substrate, indicating that the MsrB domain had a much higher affinity for the substrate than the MsrA domain. Our study reveals the first structure of the MsrAB by providing insights into the formation of a disulphide bridge in the MsrB, the structure of the linker region, and the distinct structural nature of active site of each MsrA and MsrB domain.
Insights
The first crystal structure of methionine sulphoxide reductase AB (MsrAB) from Streptococcus pneumoniae reveals its unique domain arrangement and active site. This study provides insights into enzyme function and potential drug targets.
Area of Science:
- Biochemistry
- Structural Biology
- Microbiology
Background:
- Methionine sulphoxide reductases (Msr) repair oxidized methionine, crucial for cellular function.
- Msr enzymes are classified as MsrA and MsrB based on substrate specificity.
- Some bacteria possess a fused MsrAB enzyme, combining both activities.
Purpose of the Study:
- To determine the crystal structure of MsrAB from Streptococcus pneumoniae (SpMsrAB).
- To elucidate the structural features of the fused MsrAB enzyme, including its domains, linker, and active sites.
- To investigate the substrate binding and catalytic properties of SpMsrAB.
Main Methods:
- X-ray crystallography at 2.4 Å resolution.
- Kinetic analysis of SpMsrAB activity.
- Structural analysis of enzyme-peptide complex.
Main Results:
- The first crystal structure of SpMsrAB was determined, showing an N-terminal MsrA domain and a C-terminal MsrB domain linked by a 13-residue linker.
- The MsrB domain was observed complexed with a peptide from the MsrA domain.
- Kinetic analysis revealed higher affinity of the MsrB domain for its substrate compared to the MsrA domain.
Conclusions:
- The structure provides insights into the MsrAB fusion mechanism, linker region, and distinct active sites.
- Understanding SpMsrAB structure and function can inform the development of novel antimicrobial strategies.
