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GTPase activity of a bacterial SRP-like complex
1Department of Medical Biochemistry, University of Göteborg, Sweden.
Abstract:
We have recently identified a protein (SRPM54) in Mycoplasma mycoides homologous to SRP54, a subunit of the mammalian signal recognition particle (SRP). This protein forms a complex with a mycoplasma RNA related to the RNA component of SRP. We have now demonstrated that the protein has an intrinsic GTPase activity in vitro and kinetic parameters for the enzymatic reaction have been determined. The GTPase activity was not significantly affected by the presence of the mycoplasma SRP RNA. Different regions of the SRPM54 protein were expressed as recombinant proteins in E. coli and were purified to near homogeneity. On the basis of the properties of these SRPM54 fragments two different functional domains of the protein could be distinguished. An N-terminal part was found to contain the GTPase activity and this domain had approximately the same kinetic properties as the full-length protein. Another domain corresponding to a C-terminal fragment contained the RNA binding activity as shown using an assay based on the retention of RNA-protein complexes to nitrocellulose filters.
Insights
Researchers identified a Mycoplasma mycoides protein, SRPM54, with GTPase and RNA-binding activities. This protein is homologous to mammalian signal recognition particle (SRP) subunits, offering insights into bacterial SRP function.
Area of Science:
- Molecular Biology
- Microbiology
- Biochemistry
Background:
- Mycoplasma mycoides possesses a protein (SRP M54) homologous to mammalian signal recognition particle (SRP) 54.
- This protein interacts with a mycoplasma RNA component, analogous to the SRP RNA.
Purpose of the Study:
- To characterize the biochemical properties of the SRPM54 protein.
- To identify functional domains within SRPM54.
Main Methods:
- In vitro GTPase assays were performed to determine kinetic parameters.
- Recombinant SRPM54 protein fragments were expressed and purified from E. coli.
- RNA-binding activity was assessed using nitrocellulose filter assays.
Main Results:
- SRPM54 exhibits intrinsic GTPase activity, unaffected by mycoplasma SRP RNA.
- Distinct functional domains were identified: an N-terminal GTPase domain and a C-terminal RNA-binding domain.
- Kinetic parameters for the GTPase activity were determined for the full-length protein and the N-terminal domain.
Conclusions:
- Mycoplasma SRPM54 is a functional homolog of mammalian SRP54, possessing both GTPase and RNA-binding capabilities.
- The protein's functional domains are spatially separated, with the N-terminus mediating GTP hydrolysis and the C-terminus binding RNA.
- This study elucidates the molecular mechanisms of a key component in Mycoplasma protein targeting.