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The C-terminal half of the anti-sigma factor, FlgM, becomes structured when bound to its target, sigma 28
G W Daughdrill1, M S Chadsey, J E Karlinsey
1Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
Abstract:
The interaction between the flagellum specific sigma factor, sigma 28, and its inhibitor, FlgM, was examined using multidimensional heteronuclear NMR. Here we observe that free FlgM is mostly unfolded, but about 50% of the residues become structured when bound to sigma 28. Our analysis suggests that the sigma 28 binding domain of FlgM is contained within the last 57 amino acids of the protein while the first 40 amino acids are unstructured in both the free and bound states. Genetic analysis of flgM mutants that fail to inhibit sigma 28 activity reveal amino acid changes that are also isolated to the C-terminal 57 residues of FlgM. We postulate that the lack of structure in free and bound FlgM is important to its role as an exported protein.
Insights
The flagellum sigma factor, sigma 28, binds to its inhibitor FlgM, causing FlgM to become structured. This interaction is crucial for regulating flagellar gene expression.
Area of Science:
- Bacterial flagellar assembly and regulation
- Protein structure and dynamics
- Molecular interactions
Background:
- Sigma 28 is a key transcription factor for flagellar gene expression.
- FlgM acts as an anti-sigma factor, inhibiting sigma 28 activity.
- Understanding their interaction is vital for bacterial motility regulation.
Purpose of the Study:
- To elucidate the structural basis of the sigma 28-FlgM interaction.
- To identify the key regions involved in FlgM inhibition of sigma 28.
- To explore the role of protein disorder in FlgM function.
Main Methods:
- Multidimensional heteronuclear NMR spectroscopy to determine protein structures.
- Analysis of protein-bound and unbound states.
- Genetic analysis of flgM mutants.
Main Results:
- Free FlgM is largely unstructured.
- Binding to sigma 28 induces structure in approximately 50% of FlgM residues.
- The C-terminal 57 amino acids of FlgM contain the sigma 28 binding domain.
- The N-terminal 40 amino acids remain unstructured in both states.
- Mutations affecting FlgM's inhibitory function map to the C-terminal 57 residues.
Conclusions:
- The sigma 28 binding domain of FlgM is located in its C-terminal region.
- FlgM's partial disorder is important for its function as an exported protein inhibitor.
- Structural changes upon binding regulate sigma 28 activity, impacting flagellar gene expression.