PT  - JOURNAL ARTICLE
AU  - Mangala Tawde
AU  - Abdelaziz Bior
AU  - Michael Feiss
AU  - Paul Freimuth
TI  - Disruption of nucleoid expanded conformation by toxic aberrant proteins synthesized in <em>Escherichia coli</em>
AID  - 10.1101/2021.10.06.463398
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.10.06.463398
4099  - http://biorxiv.org/content/early/2021/10/06/2021.10.06.463398.short
4100  - http://biorxiv.org/content/early/2021/10/06/2021.10.06.463398.full
AB  - Aminoglycoside antibiotics interfere with selection of cognate tRNAs during translation, resulting in the production of aberrant proteins that are the ultimate cause of the antibiotic bactericidal effect. To determine if these aberrant proteins are recognized as substrates by the cell’s protein quality control machinery, we studied whether the heat shock (HS) response was activated following exposure of Escherichia coli to the aminoglycoside kanamycin (Kan). Levels of the HS transcription factor σ32 increased about 10-fold after exposure to Kan, indicating that at least some aberrant proteins were recognized as substrates by the molecular chaperone DnaK. To investigate whether toxic aberrant proteins therefore might escape detection by the QC machinery, we studied model aberrant proteins that had a bactericidal effect when expressed in E. coli from cloned genes. As occurred following exposure to Kan, levels of σ32 were permanently elevated following expression of an acutely toxic 48-residue protein (ARF48), indicating that toxic activity and recognition by the QC machinery are not mutually exclusive properties of aberrant proteins, and that the HS response was blocked in these cells at some step downstream of σ32 stabilization. This block could result from halting of protein synthesis or from radial condensation of nucleoids, both of which occurred rapidly following ARF48 induction. Nucleoids were similarly condensed following expression of toxic aberrant secretory proteins, suggesting that transertion of inner membrane proteins, a process that expands nucleoids into an open conformation that promotes growth and gene expression, was disrupted in these cells. The 48-residue ARF48 protein would be well-suited for structural studies to further investigate the toxic mechanism of aberrant proteins.Competing Interest StatementThe authors have declared no competing interest.