Publications by Kai Johnsson | EPFL Graph Search

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Genetic regulators and environmental stimuli modulate T cell activation in autoimmunity and cancer. The enzyme co-factor tetrahydrobiopterin (BH4) is involved in the production of monoamine neurotransmitters, the generation of nitric oxide, and pain(1,2). ...

Screening of a diversity-oriented compound library led to the identification of two 6,11-dioxobenzo[f]pyrido[1,2-a]indoles (DBPI) that displayed low micromolar bactericidal activity against the Erdman strain of Mycobacterium tuberculosis in vitro. The acti ...

The SNAP-tag labeling technology provides a simple, robust, and versatile approach to the imaging of fusion proteins for a wide range of experimental applications. Owing to the specific and covalent nature of the labeling reaction, SNAP-tag is well suited ...

The ability to design proteins with high affinity and selectivity for any given small molecule is a rigorous test of our understanding of the physiochemical principles that govern molecular recognition. Attempts to rationally design ligand-binding proteins have met with little success, however, and the computational design of protein-small-molecule interfaces remains an unsolved problem. Current approaches for designing ligand-binding proteins for medical and biotechnological uses rely on raising antibodies

Aspartate is crucial for nucleotide synthesis, ammonia detoxification, and maintaining redox balance via the malate-aspartate-shuttle (MAS). To disentangle these multiple roles of aspartate metabolism, tools are required that measure aspartate concentratio ...

The lateral organization of a prototypical G protein-coupled receptor, the neurokinin-1 receptor (NK1R), was investigated in living cells by fluorescence resonance energy transfer (FRET) microscopy, taking advantage of the recently developed acyl carrier p ...

Protein turnover critically influences many biological functions, yet methods have been lacking to assess this parameter in vivo. Here, we demonstrate how chemical labeling of SNAP-tag fusion proteins can be exploited to measure the half-life of resident i ...

The specific and covalent labeling of the protein HaloTag with fluorescent probes in living cells makes it a powerful tool for bioimaging. However, the irreversible attachment of the probe to HaloTag precludes imaging applications that require transient bi ...

The study of membranes is at a turning point. New theories about membrane structure and function have recently been proposed, however, new technologies, combining chemical, physical, and biochemical approaches are necessary to test these hypotheses. In par ...

Rhodamines are the most important class of fluorophores for applications in live-cell fluorescence microscopy. This is mainly because rhodamines exist in a dynamic equilibrium between a fluorescent zwitterion and a nonfluorescent but cell-permeable spirocy ...

Super-resolution fluorescence microscopy is a powerful tool to visualize biomolecules and cellular structures at the nanometer scale. Employing these techniques in living cells has opened up the possibility to study dynamic processes with unprecedented spa ...

Ratiometric biosensors employing Forster Resonance Energy Transfer (FRET) enable the real-time tracking of metabolite dynamics. Here, we introduce an approach for generating a FRET-based biosensor in which changes in apparent FRET efficiency rely on the an ...

Mitochondria require nicotinamide adenine dinucleotide (NAD(+)) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD(+) transporters have been identified in yeast and plants(1,2), but thei ...

The measurement of tissue and cell oxygenation is important for understanding cell metabolism. We have addressed this problem with a novel optical technique, called triplet imaging, that exploits oxygen-induced triplet lifetime changes and is compatible with a variety of fluorophores. A modulated excitation of varying pulse widths allows the extraction of the lifetime of the essentially dark triplet state using a high-fluorescence signal intensity. This enables the monitoring of fast kinetics of oxygen conc

Cytochrome c peroxidase (CCP) from Saccharomyces cerevisiae was subjected to directed mol. evolution to generate mutants with increased activity against the classical peroxidase substrate, guaiacol, thus changing the substrate specificity of CCP from the protein, cytochrome c, to a small org. mol. After 3 rounds of DNA shuffling and screening, mutants were isolated which possessed a 300-fold increased activity against guaiacol and an up to 1000-fold increased specificity for this substrate relative to that

We introduce three assays for analyzing ligand-receptor interactions based on the specific conjugation of ligands to SNAP-tag fusion proteins. Conjugation of ligands to different SNAP-tag fusions permits the validation of suspected interactions in cell ext ...

The ability to specifically attach chemical probes to individual proteins represents a powerful approach to the study and manipulation of protein function in living cells. It provides a simple, robust and versatile approach to the imaging of fusion proteins in a wide range of experimental settings. However, a potential drawback of detection using chemical probes is the fluorescence background from unreacted or nonspecifically bound probes. In this report we present the design and application of novel fluoro

Phenylketonuria (PKU) is a rare metabolic disorder causing elevated phenylalanine (PHE) levels requiring lifelong dietary or pharmacological management and regular monitoring. Current PHE monitoring methods, such as tandem mass spectrometry (FIA-MS/MS), are laboratory and sample transport-dependent, leading to delays in obtaining results. This highlights the need for accessible point-of-care (PoC) solutions. Building on a previously developed bioluminescence-based PHE quantification method, we created a PoC

Fluorescent biosensors enable the study of cell physiology with spatiotemporal resolution; yet, most biosensors suffer from relatively low dynamic ranges. Here, we introduce a family of designed Forster resonance energy transfer (FRET) pairs with near-quan ...

Attempts to create novel ligand-binding proteins often focus on formation of a binding pocket with shape complementarity against the desired ligand (particularly for compounds that lack distinct polar moieties). Although designed proteins often exhibit bin ...

Kai Johnsson

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The metabolite BH4 controls T cell proliferation in autoimmunity and cancer

6,11-Dioxobenzo[f]pyrido[1,2-a]indoles Kill Mycobacterium tuberculosis by Targeting Iron-Sulfur Protein Rv0338c (IspQ), A Putative Redox Sensor

Substrates for Improved Live-Cell Fluorescence Labeling of SNAP-tag

Computational design of ligand-binding proteins with high affinity and selectivity

AspSnFR: A genetically encoded biosensor for real-time monitoring of aspartate in live cells

FRET imaging reveals that functional neurokinin-1 receptors are monomeric and reside in membrane microdomains of live cells

Measuring In Vivo Protein Half-Life

Exchangeable HaloTag Ligands for Super-Resolution Fluorescence Microscopy

Chemical Biology Approaches to Membrane Homeostasis and Function

Systematic Tuning of Rhodamine Spirocyclization for Super-resolution Microscopy

Small-Molecule Fluorescent Probes for Live-Cell Super-Resolution Microscopy

Fluorogenic Rhodamine-Based Chemigenetic Biosensor for Monitoring Cellular NADPH Dynamics

SLC25A51 is a mammalian mitochondrial NAD(+) transporter

Triplet imaging of oxygen consumption during the contraction of a single smooth muscle cell (A7r5)

Directed molecular evolution of cytochrome c peroxidase

Exploiting Ligand-Protein Conjugates to Monitor Ligand-Receptor Interactions

Development of SNAP-tag fluorogenic probes for wash-free fluorescence imaging

Real-Life Application of a Point-of-Care Biosensor for Phenylalanine in Patients With Phenylketonuria

A general method for the development of multicolor biosensors with large dynamic ranges

Unintended specificity of an engineered ligand-binding protein facilitated by unpredicted plasticity of the protein fold