Insights into histidine kinase activation mechanisms from the monomeric blue light sensor EL346

Igor Dikiy, Uthama R. Edupuganti, Rinat R. Abzalimov, Peter P. Borbat, Madhur Srivastava, Jack H. Freed, Kevin H. Gardner

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Translation of environmental cues into cellular behavior is a necessary process in all forms of life. In bacteria, this process frequently involves two-component systems in which a sensor histidine kinase (HK) autophosphorylates in response to a stimulus before subsequently transferring the phosphoryl group to a response regulator that controls downstream effectors. Many details of the molecular mechanisms of HK activation are still unclear due to complications associated with the multiple signaling states of these large, multidomain proteins. To address these challenges, we combined complementary solution biophysical approaches to examine the conformational changes upon activation of a minimal, blue-light-sensing histidine kinase from Erythrobacter litoralis HTCC2594, EL346. Our data show that multiple conformations coexist in the dark state of EL346 in solution, which may explain the enzyme's residual dark-state activity. We also observe that activation involves destabilization of the helices in the dimerization and histidine phosphotransfer-like domain, where the phosphoacceptor histidine resides, and their interactions with the catalytic domain. Similar light-induced changes occur to some extent even in constitutively active or inactive mutants, showing that light sensing can be decoupled from activation of kinase activity. These structural changes mirror those inferred by comparing X-ray crystal structures of inactive and active HK fragments, suggesting that they are at the core of conformational changes leading to HK activation. More broadly, our findings uncover surprising complexity in this simple system and allow us to outline a mechanism of the multiple steps of HK activation.

Original languageEnglish (US)
Pages (from-to)4963-4972
Number of pages10
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number11
StatePublished - 2019


  • ESR spectroscopy
  • HDX-MS
  • Photoreceptor
  • Sensor histidine kinase
  • Two-component system

ASJC Scopus subject areas

  • General


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