Academic Appointments

  • Basic Life Science Research Associate, Biology

All Publications

  • A genetically encoded Forster resonance energy transfer sensor for monitoring in vivo trehalose-6-phosphate dynamics ANALYTICAL BIOCHEMISTRY Peroza, E. A., Ewald, J. C., Parakkal, G., Skotheim, J. M., Zamboni, N. 2015; 474: 1-7


    Trehalose-6-phosphate is a pivotal regulator of sugar metabolism, growth, and osmotic equilibrium in bacteria, yeasts, and plants. To directly visualize the intracellular levels of intracellular trehalose-6-phosphate, we developed a series of specific Förster resonance energy transfer (FRET) sensors for in vivo microscopy. We demonstrated real-time monitoring of regulation in the trehalose pathway of Escherichia coli. In Saccharomyces cerevisiae, we could show that the concentration of free trehalose-6-phosphate during growth on glucose is in a range sufficient for inhibition of hexokinase. These findings support the hypothesis of trehalose-6-phosphate as the effector of a negative feedback system, similar to the inhibition of hexokinase by glucose-6-phosphate in mammalian cells and controlling glycolytic flux.

    View details for DOI 10.1016/j.ab.2014.12.019

    View details for Web of Science ID 000352170800001

  • Cell Size Control in Yeast CURRENT BIOLOGY Turner, J. J., Ewald, J. C., Skotheim, J. M. 2012; 22 (9): R350-R359


    Cell size is an important adaptive trait that influences nearly all aspects of cellular physiology. Despite extensive characterization of the cell-cycle regulatory network, the molecular mechanisms coupling cell growth to division, and thereby controlling cell size, have remained elusive. Recent work in yeast has reinvigorated the size control field and suggested provocative mechanisms for the distinct functions of setting and sensing cell size. Further examination of size-sensing models based on spatial gradients and molecular titration, coupled with elucidation of the pathways responsible for nutrient-modulated target size, may reveal the fundamental principles of eukaryotic cell size control.

    View details for DOI 10.1016/j.cub.2012.02.041

    View details for Web of Science ID 000303967600019

    View details for PubMedID 22575477

  • Engineering Genetically Encoded Nanosensors for Real-Time In Vivo Measurements of Citrate Concentrations PLOS ONE Ewald, J. C., Reich, S., Baumann, S., Frommer, W. B., Zamboni, N. 2011; 6 (12)


    Citrate is an intermediate in catabolic as well as biosynthetic pathways and is an important regulatory molecule in the control of glycolysis and lipid metabolism. Mass spectrometric and NMR based metabolomics allow measuring citrate concentrations, but only with limited spatial and temporal resolution. Methods are so far lacking to monitor citrate levels in real-time in-vivo. Here, we present a series of genetically encoded citrate sensors based on Förster resonance energy transfer (FRET). We screened databases for citrate-binding proteins and tested three candidates in vitro. The citrate binding domain of the Klebsiella pneumoniae histidine sensor kinase CitA, inserted between the FRET pair Venus/CFP, yielded a sensor highly specific for citrate. We optimized the peptide linkers to achieve maximal FRET change upon citrate binding. By modifying residues in the citrate binding pocket, we were able to construct seven sensors with different affinities spanning a concentration range of three orders of magnitude without losing specificity. In a first in vivo application we show that E. coli maintains the capacity to take up glucose or acetate within seconds even after long-term starvation.

    View details for DOI 10.1371/journal.pone.0028245

    View details for Web of Science ID 000298171400052

    View details for PubMedID 22164251

  • In VIVO biochemistry: quantifying ion and metabolite levels in individual cells or cultures of yeast BIOCHEMICAL JOURNAL Bermejo, C., Ewald, J. C., Lanquar, V., Jones, A. M., Frommer, W. B. 2011; 438: 1-10


    Over the past decade, we have learned that cellular processes, including signalling and metabolism, are highly compartmentalized, and that relevant changes in metabolic state can occur at sub-second timescales. Moreover, we have learned that individual cells in populations, or as part of a tissue, exist in different states. If we want to understand metabolic processes and signalling better, it will be necessary to measure biochemical and biophysical responses of individual cells with high temporal and spatial resolution. Fluorescence imaging has revolutionized all aspects of biology since it has the potential to provide information on the cellular and subcellular distribution of ions and metabolites with sub-second time resolution. In the present review we summarize recent progress in quantifying ions and metabolites in populations of yeast cells as well as in individual yeast cells with the help of quantitative fluorescent indicators, namely FRET metabolite sensors. We discuss the opportunities and potential pitfalls and the controls that help preclude misinterpretation.

    View details for DOI 10.1042/BJ20110428

    View details for Web of Science ID 000294083400001

    View details for PubMedID 21793803