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Structure of a Type-1 Secretion System ABC Transporter.
Jacob L W Morgan1, Justin F Acheson1, Jochen Zimmer1
1Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, 480 Ray C. Hunt Drive, Charlottesville, VA 22908, USA.
Structure (London, England : 1993)
|February 21, 2017
Summary
Type-1 secretion systems (T1SSs) use ATP hydrolysis and complex assembly for protein secretion in Gram-negative bacteria. The structure of Aquifex aeolicus PtrD reveals a novel transport mechanism distinct from typical peptide transporters.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Type-1 secretion systems (T1SSs) are crucial for protein export across the bacterial cell envelope.
- T1SSs comprise an inner-membrane ABC transporter, a periplasmic membrane-fusion protein, and an outer-membrane porin.
- These components form a channel for translocating unfolded polypeptides.
Purpose of the Study:
- To investigate the functional requirements for T1SS-mediated protein secretion.
- To determine the structural basis of substrate translocation by the T1SS ABC transporter.
- To elucidate the mechanism of protein transport in Gram-negative bacteria.
Main Methods:
- Biochemical assays to assess the necessity of ATP hydrolysis and T1SS complex assembly for secretion.
- X-ray crystallography to determine the high-resolution structure of the AaPrtD ABC transporter.
- Structural analysis to identify key features involved in substrate binding and translocation.
Main Results:
- ATP hydrolysis and the complete assembly of the T1SS complex are essential for protein secretion.
- A 3.15-Å crystal structure of AaPrtD revealed a substrate entry window above the nucleotide-binding domains.
- Highly kinked transmembrane helices form a narrow channel, suggesting a unique transport mechanism.
Conclusions:
- The study confirms the critical roles of ATP hydrolysis and T1SS assembly in protein secretion.
- The AaPrtD structure provides insights into a novel polypeptide transport mechanism.
- This mechanism appears distinct from the canonical alternating access model used by other transporters.
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