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ADP-dependent conformational changes distinguish Mycobacterium tuberculosis SecA2 from SecA1
Nadia G D'Lima1, Carolyn M Teschke
1From the Departments of Molecular and Cell Biology and.
Abstract:
In bacteria, most secreted proteins are exported through the SecYEG translocon by the SecA ATPase motor via the general secretion or "Sec" pathway. The identification of an additional SecA protein, particularly in Gram-positive pathogens, has raised important questions about the role of SecA2 in both protein export and establishment of virulence. We previously showed in Mycobacterium tuberculosis, the causative agent of tuberculosis, the accessory SecA2 protein possesses ATPase activity that is required for bacterial survival in host macrophages, highlighting its importance in virulence. Here, we show that SecA2 binds ADP with much higher affinity than SecA1 and releases the nucleotide more slowly. Nucleotide binding also regulates movement of the precursor-binding domain in SecA2, unlike in SecA1 or conventional SecA proteins. This conformational change involving closure of the clamp in SecA2 may provide a mechanism for the cell to direct protein export through the conventional SecA1 pathway under normal growth conditions while preventing ordinary precursor proteins from interacting with the specialized SecA2 ATPase.
Insights
The accessory SecA2 protein in bacteria binds ADP tightly, regulating its function and virulence. This differs from SecA1, suggesting a specialized role in protein export and pathogen survival.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Most bacterial secreted proteins use the SecYEG translocon and SecA ATPase motor via the general secretion pathway.
- The accessory SecA2 protein, found in Gram-positive pathogens, has a crucial role in virulence and protein export.
Purpose of the Study:
- To investigate the biochemical properties and regulatory mechanisms of the SecA2 protein.
- To understand the functional differences between SecA1 and SecA2 in protein secretion and virulence.
Main Methods:
- Biochemical assays to measure ATPase activity and nucleotide binding affinity.
- Analysis of conformational changes in SecA2 upon nucleotide binding.
Main Results:
- SecA2 exhibits significantly higher affinity for ADP compared to SecA1, with slower nucleotide release.
- Nucleotide binding induces a conformational change in SecA2's precursor-binding domain, distinct from SecA1.
- This conformational regulation may differentiate SecA2's specialized export function from the general SecA1 pathway.
Conclusions:
- SecA2's unique nucleotide-binding properties suggest a regulatory mechanism for specialized protein export.
- The findings highlight SecA2's importance in bacterial virulence and survival within host macrophages.
- Understanding SecA2 function provides insights into pathogen-host interactions and potential therapeutic targets.
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