Dimerization and DNA‐dependent aggregation of the Escherichia coli nucleoid protein and chaperone CbpA |
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| Authors: | Sarah Cosgriff Kiran Chintakayala Ya Tsz A Chim Xinyong Chen Stephanie Allen Andrew L Lovering David C Grainger |
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| Institution: | 1. Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK;2. Laboratory of Biophysics and Surface Analysis, School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, UK;3. School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK |
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| Abstract: | The Escherichia coli curved DNA‐binding protein A (CbpA) is a nucleoid‐associated DNA‐binding factor and chaperone that is expressed at high levels as cells enter stationary phase. Using a combination of genetics, biochemistry, structural modelling and single‐molecule atomic force microscopy we have examined dimerization of, and DNA binding by, CbpA. Our data show that CbpA dimerization is driven by a hydrophobic surface comprising amino acid side chains W287 and L290 located on the same side of an α helix close to the C‐terminus of CbpA. Derivatives of CbpA that are unable to dimerize are also unable to bind DNA. Free in solution, CbpA can exist as either a monomer or dimer. However, when bound to DNA, CbpA forms large aggregates that can protect DNA from degradation by nucleases. These CbpA–DNA aggregates are similar in morphology to protein–DNA complexes formed by the DNA‐binding protein from starved cells (Dps), the only other stationary phase‐specific nucleoid protein. Conversely, protein–DNA complexes formed by Fis, the major growth phase nucleoid protein, have a markedly different appearance. |
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