In many gram positive bacteria, horizontal transfer and virulence are regulated by peptide-mediated cell-cell signaling. The heptapeptide cCF10 (C) activates conjugative transfer of the Enterococcus faecalis plasmid pCF10, whereas the iCF10 (I) peptide inhibits transfer. Both peptides bind to the same domain of the master transcription regulator PrgX, a repressor of transcription of the prgQ operon encoding conjugation genes. We show that repression of prgQ by PrgX tetramers requires formation of a pCF10 DNA loop where each of two PrgX DNA-binding sites is occupied by a dimer. I binding to PrgX enhances prgQ repression, while C binding has the opposite effect. Previous models suggested that differential effects of these two peptides on the PrgX oligomerization state accounted for their distinct functions. Our new results demonstrate that both peptides have similar, high-binding affinity for PrgX, and that both peptides actually promote formation of PrgX tetramers with higher DNA-binding affinity than Apo-PrgX. We propose that differences in repression ability of PrgX/peptide complexes result from subtle differences in the structures of DNA-bound PrgX/peptide complexes. Changes in the induction state of a donor cell likely results from replacement of one type of DNA-bound peptide/PrgX tetramer with the other.
Bibliographical noteFunding Information:
We thank Dawn Manias, Thinh Le, and Chris Johnson for helpful discussions and assistance with protein preparation and EMSAs and Larry Wackett, James Christenson and Tony Dodge for help with size exclusion chromatography. This project was supported by grants GM118079, GM081888 and GM049530 from the National Institutes of Health, and a Bridge Grant from the University of Minnesota Foundation. BKK was a trainee under Biotechnology Training grant T32GM0008347 from the National Institutes of Health.
© 2017 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.
- RRNPP transcription factor
- antibiotic resistance
- bacterial transcription
- cell signaling
- gene transfer
- gram positive bacteria
- protein-nucleic interaction