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A structural role for the PHP domain in E. coli DNA polymerase III.


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Authors

Barros, Tiago 
Guenther, Joel 
Kelch, Brian 
Anaya, Jordan 
Prabhakar, Arjun 

Abstract

BACKGROUND: In addition to the core catalytic machinery, bacterial replicative DNA polymerases contain a Polymerase and Histidinol Phosphatase (PHP) domain whose function is not entirely understood. The PHP domains of some bacterial replicases are active metal-dependent nucleases that may play a role in proofreading. In E. coli DNA polymerase III, however, the PHP domain has lost several metal-coordinating residues and is likely to be catalytically inactive. RESULTS: Genomic searches show that the loss of metal-coordinating residues in polymerase PHP domains is likely to have coevolved with the presence of a separate proofreading exonuclease that works with the polymerase. Although the E. coli Pol III PHP domain has lost metal-coordinating residues, the structure of the domain has been conserved to a remarkable degree when compared to that of metal-binding PHP domains. This is demonstrated by our ability to restore metal binding with only three point mutations, as confirmed by the metal-bound crystal structure of this mutant determined at 2.9 Å resolution. We also show that Pol III, a large multi-domain protein, unfolds cooperatively and that mutations in the degenerate metal-binding site of the PHP domain decrease the overall stability of Pol III and reduce its activity. CONCLUSIONS: While the presence of a PHP domain in replicative bacterial polymerases is strictly conserved, its ability to coordinate metals and to perform proofreading exonuclease activity is not, suggesting additional non-enzymatic roles for the domain. Our results show that the PHP domain is a major structural element in Pol III and its integrity modulates both the stability and activity of the polymerase.

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Keywords

Amino Acid Sequence, Binding Sites, Catalytic Domain, Crystallography, X-Ray, DNA Polymerase III, Escherichia coli, Escherichia coli Proteins, Metals, Molecular Sequence Data, Mutation, Protein Stability, Protein Structure, Tertiary, Sequence Alignment

Journal Title

BMC Struct Biol

Conference Name

Journal ISSN

1472-6807
1472-6807

Volume Title

Publisher

Springer Science and Business Media LLC