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Diversification of DNA-Binding Specificity by Permissive and Specificity-Switching Mutations in the ParB/Noc Protein Family.

ABSTRACT: Specific interactions between proteins and DNA are essential to many biological processes. Yet, it remains unclear how the diversification in DNA-binding specificity was brought about, and the mutational paths that led to changes in specificity are unknown. Using a pair of evolutionarily related DNA-binding proteins, each with a different DNA preference (ParB [Partitioning Protein B] and Noc [Nucleoid Occlusion Factor], which both play roles in bacterial chromosome maintenance), we show that specificity is encoded by a set of four residues at the protein-DNA interface. Combining X-ray crystallography and deep mutational scanning of the interface, we suggest that permissive mutations must be introduced before specificity-switching mutations to reprogram specificity and that mutational paths to new specificity do not necessarily involve dual-specificity intermediates. Overall, our results provide insight into the possible evolutionary history of ParB and Noc and, in a broader context, might be useful for understanding the evolution of other classes of DNA-binding proteins.

SUBMITTER: Jalal ASB

PROVIDER: S-EPMC7383237 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Diversification of DNA-binding specificity via permissive and specificity-switching mutations in the ParB/Noc protein family

Project description:Specific interactions between proteins and DNA are essential to many biological processes. Yet it remains unclear how the diversification in DNA-binding specificity was brought about, and what were the mutational paths that led to changes in specificity. Using a pair of evolutionarily related DNA-binding proteins, each with a different DNA preference (ParB and Noc: both having roles in bacterial chromosome maintenance), we show that specificity is encoded by a set of four residues at the protein-DNA interface. Combining X-ray crystallography and deep mutational scanning of the interface, we suggest that permissive mutations must be introduced before specificity-switching mutations to reprogram specificity, and that mutational paths to a new specificity do not necessarily involve dual-specificity intermediates. Overall, our results provide insight into the possible evolutionary history of ParB and Noc, and in a broader context, might be useful in understanding the evolution of other classes of DNA-binding proteins.

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Diversification of DNA-binding specificity via permissive and specificity-switching mutations in the ParB/Noc protein family

Project description:Diversification of DNA-binding specificity via permissive and specificity-switching mutations in the ParB/Noc protein family

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Project description:Transcription factor-DNA interactions and their specificities have been described for many different classes of transcription factor families. However, heterodimeric transcription factor complexes still remain poorly characterised. The basic-Helix-Loop-Helix (bHLH) transcription factor family is one of the largest transcription factor families that typically bind DNA though a degenerate CANNTG elements as heterodimers or homodimers. Here we characterise the DNA binding of the bHLH - Per-Arnt-Sim (PAS) (bHLH-PAS) domain containing transcription factor family using SELEX-high-throughput sequencing coupled with quantitative computational modelling analysis. We show that most dimeric bHLH-PAS transcription factors bind to distinct core NNCGTG response elements but bind over a much larger footprint than previously characterised. Modelled DNA-protein interactions were found to correlate with structural analysis, DNA shape predictions and in vivo transcription factor occupancy.

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Permissive zones for the centromere-binding protein ParB on the Caulobacter crescentus chromosome

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Project description:Transcription factors activate their target genes by binding to specific response elements. Many transcription factor families evolved from a common ancestor by gene duplication and subsequent divergent evolution. Members of the p53 family, which play key roles in cell-cycle control and development, share conserved DNA binding and oligomerisation domains but exhibit distinct functions. In this study, the molecular basis of the functional divergence of related transcription factors was investigated.We characterised the DNA-binding specificity and oligomerisation properties of human p53, p63 and p73, as well as p53 from other organisms using novel biophysical approaches. All p53 family members bound DNA cooperatively as tetramers with high affinity. Despite structural differences in the oligomerisation domain, the dissociation constants of the tetramers was in the low nanomolar range for all family members, indicating that the strength of tetramerisation was evolutionarily conserved. However, small differences in the oligomerisation properties were observed, which may play a regulatory role. Intriguingly, the DNA-binding specificity of p53 family members was highly conserved even for evolutionarily distant species. Additionally, DNA recognition was only weakly affected by CpG methylation. Prediction of p53/p63/p73 binding sites in the genome showed almost complete overlap between the different homologs.Diversity of biological function of p53 family members is not reflected in differences in sequence-specific DNA binding. Hence, additional specificity factors must exist, which allowed the acquisition of novel functions during evolution while preserving original roles.

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