The universally conserved ATPase as mediator of cellular stress response

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YchF is a universally conserved ATPase of unknown function, which is classified as a member of the translation-factor like GTPases, although it preferentially hydrolyzes ATP over GTP. Ribosome binding was shown for E. coli and Trypanosoma cruzii YchF, but the possible impact on protein synthesis is unknown so far. The human YchF homologue Ola1 does not seem to bind to ribosomes and instead is implicated in the post-translational regulation of the oxidative stress respsonse and in tumour development. This latter proposal is in line with the observed up-regulation of Ola1 in many tumours. However, the molecular mechanisms of Ola1 function and possible interaction partners are entirely unknown. Our data on the function of this highly conserved protein in E. coli demonstrate that YchF inhibits the oxidative stress response. Inhibition is not caused by a transcriptional or translational down-regulation of major oxidative stress response proteins (OxyR, KatG), but rather by a direct inhibition of catalase activity (Wenk et al., 2012). A direct interaction between YchF and the catalases/peroxidases KatG, KatE and AhpCF was demonstrated by site-specific cross-linking approaches and by mass spectrometry. These data suggest that YchF regulates the oxidative stress response by a so far unknown post-translational inhibition of major stress proteins. Phosphorylation/ dephosphorylation of YchF and its ATPase activity appear to be important for this inhibitory function. Our data suggest that E. coli YchF and human Ola1 have apparently very similar function and act as universally conserved inhibitors of the oxidative stress response. Our aim is to identify the targets of YchF mediated inhibition and to disclose the underlying molecular mechanism. The easily amendable model organisms E. coli and S. cerevisiae will be employed to determine the YchF interactome in response to oxidative stress and to reveal the biochemical and molecular framework of YchF-dependent inhibition of target proteins. This includes the detailed analyses on YchF expression and modification in response to oxidative stress. Considering the postulated involvement of Ola1 in tumour-development and metastasis, we plan to extend our analyses to human cell lines, once we have established a solid framework of YchF function in E. coli/S. cerevisiae. This knowledge transfer will be the main focus of an extension proposal.