Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 7, Pages E398-E405Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1113277108
Keywords
Archaea; molecular evolution; replication protein A
Categories
Funding
- Wellcome Trust
- Biotechnology and Biological Sciences Research Council [BB/S/B14450]
- US Department of Health and Human Services
- Biotechnology and Biological Sciences Research Council [BBS/B/14426] Funding Source: researchfish
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ssDNA-binding proteins (SSBs) based on the oligonucleotide-binding fold are considered ubiquitous in nature and play a central role in many DNA transactions including replication, recombination, and repair. We demonstrate that the Thermoproteales, a clade of hyperthermophilic Crenarchaea, lack a canonical SSB. Instead, they encode a distinct ssDNA-binding protein that we term ThermoDBP, exemplified by the protein Ttx1576 from Thermoproteus tenax. ThermoDBP binds specifically to ssDNA with low sequence specificity. The crystal structure of Ttx1576 reveals a unique fold and a mechanism for ssDNA binding, consisting of an extended cleft lined with hydrophobic phenylalanine residues and flanked by basic amino acids. Two ssDNA-binding domains are linked by a coiled-coil leucine zipper. ThermoDBP appears to have displaced the canonical SSB during the diversification of the Thermoproteales, a highly unusual example of the loss of a ubiquitous protein during evolution.
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