Linkage between fitness of yeast cells and adenylate kinase catalysis

Enzymes have evolved with highly specific values of their catalytic parameters kcat and KM. This poses fundamental biological questions about the selection pressures responsible for evolutionary tuning of these parameters. Here we are address these questions for the enzyme adenylate kinase (Adk) in eukaryotic yeast cells. A plasmid shuffling system was developed to allow quantification of relative fitness (calculated from growth rates) of yeast in response to perturbations of Adk activity introduced through mutations. Biophysical characterization verified that all variants studied were properly folded and that the mutations did not cause any substantial differences to thermal stability. We found that cytosolic Adk is essential for yeast viability in our strain background and that viability could not be restored with a catalytically dead, although properly folded Adk variant. There exist a massive overcapacity of Adk catalytic activity and only 12% of the wild type kcat is required for optimal growth at the stress condition 20°C. In summary, the approach developed here has provided new insights into the evolutionary tuning of kcat for Adk in a eukaryotic organism. The developed methodology may also become useful for uncovering new aspects of active site dynamics and also in enzyme design since a large library of enzyme variants can be screened rapidly by identifying viable colonies

Quantitative NMR analysis of Erk activity and inhibition by U0126 in a panel of patient-derived colorectal cancer cell lines

We comparatively analyzed the basal activity of extra-cellular signal-regulated kinase (Erk1/2) in lysates of 10 human colorectal cancer cell lines by semi-quantitative Western blotting and time-resolved NMR spectroscopy. Both methods revealed heterogeneous levels of endogenous Erk1/2 activities in a highly consistent manner. Upon treatment with U0126, an inhibitor of mitogen-activated protein kinase kinase (MEK) acting upstream of Erk1/2, Western-blotting and NMR congruently reported specific modulations of cellular phospho-Erk levels that translated into reduced kinase activities. Results obtained in this study highlight the complementary nature of antibody- and NMR-based phospho-detection techniques. They further exemplify the usefulness of time-resolved NMR measurements in providing fast and quantitative readouts of kinase activities and kinase inhibitor efficacies in native cellular environments. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012). © 2013 Elsevier B.V