Title Gly184 of the Escherichia coli cAMP receptor protein provides optimal context for both DNA binding and RNA polymerase interaction
Author Matt N. Hicks1, Sanjiva Gunasekara1, Jose Serate2, Jin Park3, Pegah Mosharaf1, Yue Zhou1, Jin-Won Lee4, and Hwan Youn1*
Address 1Department of Biology, California State University Fresno, California 93740, USA, 2Department of Bacteriology, University of Wisconsin-Madison, Wisconsin 53706, USA, 3Department of Computer Science, California State University Fresno, California 93740, USA, 4Department of Life Science and Institute for Natural Sciences, Hanyang University, Seoul 04763, Republic of Korea
Bibliography Journal of Microbiology, 55(10),816-822, 2017,
DOI 10.1007/s12275-017-7266-x
Key Words CRP, Escherichia coli, Gly184, DNA binding, transcriptional activation, conformational flexibility
Abstract The Escherichia coli cAMP receptor protein (CRP) utilizes the helix-turn-helix motif for DNA binding. The CRP’s recognition helix, termed F-helix, includes a stretch of six amino acids (Arg180, Glu181, Thr182, Val183, Gly184, and Arg185) for direct DNA contacts. Arg180, Glu181 and Arg185 are known as important residues for DNA binding and specificity, but little has been studied for the other residues. Here we show that Gly184 is another F-helix residue critical for the transcriptional activation function of CRP. First, glycine was repeatedly selected at CRP position 184 for its unique ability to provide wild type-level transcriptional activation activity. To dissect the glycine requirement, wild type CRP and mutants G184A, G184F, G184S, and G184Y were purified and their in vitro DNA-binding activity was measured. G184A and G184F displayed reduced DNA binding, which may explain their low transcriptional activation activity. However, G184S and G184Y displayed apparently normal DNA affinity. Therefore, an additional factor is needed to account for the diminished transcriptional activation function in G184S and G184Y, and the best explanation is perturbations in their interaction with RNA polymerase. The fact that glycine is the smallest amino acid could not fully warrant its suitability, as shown in this study. We hypothesize that Gly184 fulfills the dual functions of DNA binding and RNA polymerase interaction by conferring conformational flexibility to the F-helix.