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Defining the mRNA recognition signature of a bacterial toxin protein

Marc A Schureck1, Jack A Dunkle1, Tatsuya Maehigashi1

  • 1Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.

Proceedings of the National Academy of Sciences of the United States of America
|October 29, 2015
PubMed

Insights

Bacterial type II toxins cleave messenger RNAs (mRNAs) at the ribosome. This study reveals how the HigB toxin specifically recognizes mRNA sequences, with the third nucleotide being the most critical for cleavage.

Area of Science:

  • Molecular Biology
  • Bacteriology
  • Structural Biology

Background:

  • Bacteria utilize type II toxins to degrade messenger RNAs (mRNAs) at the ribosome, regulating translation, growth, and survival.
  • Ribosome-dependent toxins recognize specific three-nucleotide codons in the aminoacyl (A) site, but the mechanisms of substrate specificity are not fully understood.

Purpose of the Study:

  • To identify the key features enabling the host inhibition of growth B (HigB) toxin to recognize and cleave specific mRNA sequences at the ribosome.
  • To elucidate the structural basis of HigB toxin's nucleotide recognition within the ribosomal A site.

Main Methods:

  • X-ray crystallography was employed to determine the structures of the HigB toxin bound to different codons on the ribosome.
  • Analysis of nucleotide-protein and nucleotide-rRNA interactions within the ribosomal A site.

Main Results:

  • HigB toxin utilizes a nucleotide recognition loop, similar to microbial RNases, to identify cytosine or adenosine at the second A-site position.
  • A specific pocket, formed by a single HigB residue and 16S rRNA residue C1054, dictates adenosine specificity at the third A-site nucleotide.
  • The interaction with the third A-site nucleotide is the primary determinant for mRNA cleavage by ribosome-dependent toxins.

Conclusions:

  • The study clarifies the molecular basis of mRNA substrate specificity for the HigB toxin.
  • Findings highlight the crucial role of the third A-site nucleotide in dictating toxin-mediated mRNA cleavage.
  • This research provides insights into bacterial toxin mechanisms and potential targets for antimicrobial strategies.
Keywords:
RNasesprotein synthesisribosomestringent responsetoxin–antitoxin systems

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