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Programmed Ribosomal Frameshifting Generates a Copper Transporter and a Copper Chaperone from the Same Gene.
Sezen Meydan1, Dorota Klepacki1, Subbulakshmi Karthikeyan1
1Center for Biomolecular Sciences-m/c 870, University of Illinois at Chicago, 900 S. Ashland Avenue, Chicago, IL 60607, USA.
Molecular Cell
|January 21, 2017
Summary
In Escherichia coli, a single gene produces both the copper transporter CopA and its chaperone, CopA(Z), via programmed ribosomal frameshifting. This mechanism helps cells survive toxic copper levels.
Area of Science:
- Molecular Biology
- Microbiology
- Biochemistry
Background:
- Metal efflux pumps, like copper transporter CopA in Escherichia coli, are crucial for maintaining cellular ion homeostasis.
- Chaperone proteins typically support these transporters by scavenging metal ions, but CopA's specific chaperone was previously unidentified.
Purpose of the Study:
- To identify the chaperone for the copper ion transporter CopA in Escherichia coli.
- To elucidate the mechanism of CopA chaperone production and its role in copper homeostasis.
Main Methods:
- Analysis of the Escherichia coli copA gene and its translated products.
- Investigation of programmed ribosomal frameshifting during copA translation.
- Identification of mRNA elements (slippery sequence, pseudoknot) and nascent chain interactions influencing frameshifting efficiency.
Main Results:
- The CopA chaperone is expressed from the same gene as the CopA transporter in E. coli.
- Programmed ribosomal frameshifting in the copA mRNA generates a 70 amino acid polypeptide, CopA(Z), which functions as the chaperone.
- High frameshifting efficiency is mediated by a slippery sequence, an mRNA pseudoknot, and the nascent CopA chain.
- Similar frameshifting elements are conserved in bacterial copA genes and the human ATP7B gene.
Conclusions:
- A single gene encodes both the copper transporter and its chaperone in E. coli through programmed ribosomal frameshifting.
- This novel mechanism of chaperone production enhances cellular survival in toxic copper environments.
- The identified frameshifting elements and mechanism are conserved across species, including humans, suggesting a fundamental biological role.
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