Clamp loaders are AAA+ ATPases that load sliding clamps onto DNA. We mapped the mutational sensitivity of the T4 bacteriophage sliding clamp and clamp loader by deep mutagenesis, and found that residues not involved in catalysis or binding display remarkable tolerance to mutation. An exception is a glutamine residue in the AAA+ module (Gln 118) that is not located at a catalytic or interfacial site. Gln 118 forms a hydrogen-bonded junction in a helical unit that we term the central coupler, because it connects the catalytic centers to DNA and the sliding clamp. A suppressor mutation indicates that hydrogen bonding in the junction is important, and molecular dynamics simulations reveal that it maintains rigidity in the central coupler. The glutamine-mediated junction is preserved in diverse AAA+ ATPases, suggesting that a connected network of hydrogen bonds that links ATP molecules is an essential aspect of allosteric communication in these proteins.
All data generated or analyzed during this study are included in the manuscript and supporting files. Source data files with raw counts and relative fitness scores are included.
- Subu Subramanian
- Kent Gorday
- Peter Ren
- Xiao Ran Luo
- John Kuriyan
- Matthew R Orellana
- Kent Gorday
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- James M Berger, Johns Hopkins University School of Medicine, United States
- Received: January 4, 2021
- Accepted: April 3, 2021
- Accepted Manuscript published: April 13, 2021 (version 1)
© 2021, Subramanian et al.
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