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Zhou H, Sathyamoorthy B, Stelling A, Xu Y, Xue Y, Pigli YZ, Case DA, Rice PA, Al-Hashimi HM. Characterizing Watson-Crick versus Hoogsteen Base Pairing in a DNA-Protein Complex Using Nuclear Magnetic Resonance and Site-Specifically 13C- and 15N-Labeled DNA. Biochemistry 2019; 58:1963-1974. [PMID: 30950607 DOI: 10.1021/acs.biochem.9b00027] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
A( syn)-T and G( syn)-C+ Hoogsteen base pairs in protein-bound DNA duplexes can be difficult to resolve by X-ray crystallography due to ambiguous electron density and by nuclear magnetic resonance (NMR) spectroscopy due to poor chemical shift dispersion and size limitations with solution-state NMR spectroscopy. Here we describe an NMR strategy for characterizing Hoogsteen base pairs in protein-DNA complexes, which relies on site-specifically incorporating 13C- and 15N-labeled nucleotides into DNA duplexes for unambiguous resonance assignment and to improve spectral resolution. The approach was used to resolve the conformation of an A-T base pair in a crystal structure of an ∼43 kDa complex between a 34 bp duplex DNA and the integration host factor (IHF) protein. In the crystal structure (Protein Data Bank entry 1IHF ), this base pair adopts an unusual Hoogsteen conformation with a distorted sugar backbone that is accommodated by a nearby nick used to aid in crystallization. The NMR chemical shifts and interproton nuclear Overhauser effects indicate that this base pair predominantly adopts a Watson-Crick conformation in the intact DNA-IHF complex under solution conditions. Consistent with these NMR findings, substitution of 7-deazaadenine at this base pair resulted in only a small (∼2-fold) decrease in the IHF-DNA binding affinity. The NMR strategy provides a new approach for resolving crystallographic ambiguity and more generally for studying the structure and dynamics of protein-DNA complexes in solution.
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Affiliation(s)
- Huiqing Zhou
- Department of Biochemistry , Duke University School of Medicine , Durham , North Carolina 27710 , United States
| | - Bharathwaj Sathyamoorthy
- Department of Chemistry , Indian Institute of Science Education and Research Bhopal , Bhopal 462066 , India
| | - Allison Stelling
- Department of Biochemistry , Duke University School of Medicine , Durham , North Carolina 27710 , United States
| | - Yu Xu
- Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States
| | - Yi Xue
- Tsinghua-Peking Center for Life Sciences, School of Life Sciences , Tsinghua University , Beijing 100084 , China
| | - Ying Zhang Pigli
- Biochemistry and Molecular Biology , The University of Chicago , Chicago , Illinois 60637 , United States
| | - David A Case
- Department of Chemistry and Chemical Biology , Rutgers University , Piscataway , New Jersey 08854 , United States
| | - Phoebe A Rice
- Biochemistry and Molecular Biology , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Hashim M Al-Hashimi
- Department of Biochemistry , Duke University School of Medicine , Durham , North Carolina 27710 , United States.,Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States
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