Publications de Kai Johnsson | EPFL Graph Search

Improving split-HaloTag through computational protein engineering

Split-HaloTag can be used to transform transient molecular interactions into permanent marks through chemical labeling, thereby enabling the recording of transient physiological events in individual cells. However, applications of split-HaloTag-based recor ...

WILEY2025

Exploiting Covalent Chemical Labeling with Self-Labeling Proteins

Kai Johnsson

The visualization and manipulation of proteins in live cells are critical for studying complex biological processes. Self-labeling proteins do so by enabling the specific and covalent attachment of synthetic probes, offering unprecedented flexibility in th ...

Annual Reviews2025

Molecular recording of cellular protein kinase activity with chemical labeling

Kai Johnsson

Protein kinases control most cellular processes and aberrant kinase activity is involved in numerous diseases. Here we introduce molecular recorders of kinase activities for later analysis to investigate the link between specific kinase activities and cell ...

2025

A Silicon Rhodamine-fused Glibenclamide to Label and Detect Malaria-infected Red Blood Cells

Kai Johnsson, Luc Reymond, Johannes Broichhagen

The malaria parasite Plasmodium falciparum affects the lives of millions of people worldwide every year. The detection of replicating parasites within human red blood cells is of paramount importance, requiring appropriate diagnostic tools. Herein, we desi ...

WILEY-V C H VERLAG GMBH2025

SNAP-tag2 for faster and brighter protein labeling

Kai Johnsson

SNAP-tag is a powerful tool for labeling proteins with synthetic fluorophores in bioimaging. However, its utility in live-cell applications can be constrained by its relatively slow labeling kinetics and the limited cell permeability of its substrates. Her ...

2025

Recording physiological history of cells with chemical labeling

Kai Johnsson, Julien Hiblot, Ling Hai

Recordings of the physiological history of cells provide insights into biological processes, yet obtaining such recordings is a challenge. To address this, we introduce a method to record transient cellular events for later analysis. We designed proteins t ...

American Association for the Advancement of Science2024

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

Kai Johnsson

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 ...

CELL PRESS2024

Metal-free introduction of primary sulfonamide into electron-rich aromatics

Kai Johnsson

We report herein a direct and practical synthesis of arylsulfonamides from electron-rich aromatic compounds by using in situ generated N-sulfonylamine as the active electrophile. Substrates include derivatives of aniline, indole, pyrrole, furan, styrene an ...

ROYAL SOC CHEMISTRY2024

Fluorogenic Rhodamine-Based Chemigenetic Biosensor for Monitoring Cellular NADPH Dynamics

Kai Johnsson

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 ...

AMER CHEMICAL SOC2024

Low temperature and mTOR inhibition favor stem cell maintenance in human keratinocyte cultures

Fahd Azzabi Zouraq, Kai Johnsson, Yann Barrandon, Ariane Rochat, Thomas Michael Braschler, Johannes Alexander Mosig, Jean-Baptiste Bureau, Mako Kamiya

Adult autologous human epidermal stem cells can be extensively expanded ex vivo for cell and gene therapy. Identifying the mechanisms involved in stem cell maintenance and defining culture conditions to maintain stemness is critical, because an inadequate ...

WILEY2023

Chemical Probe for Imaging of Polo-like Kinase 4 and Centrioles

Kai Johnsson, Luc Reymond, Pierre Gönczy, Aleksandar Salim, Georgios Hatzopoulos

Polo-like kinase (Plk4) is a serine/threonine-proteinkinase thatis essential for biogenesis of the centriole organelle and is enrichedat centrioles. Herein, we introduce Cen-TCO, a chemical probe basedon the Plk4 inhibitor centrinone, to image Plk4 and cen ...

AMER CHEMICAL SOC2023

Absence of mitochondrial SLC25A51 enhances PARP1-dependent DNA repair by increasing nuclear NAD(+) levels

Kai Johnsson

Though the effect of the recently identified mitochondrial NAD(+) transporter SLC25A51 on glucose metabolism has been described, its contribution to other NAD(+)-dependent processes throughout the cell such as ADP-ribosylation remains elusive. Here, we rep ...

OXFORD UNIV PRESS2023

Low temperature and mTOR inhibition favor human epidermal stem cell maintenance

Juan Ramon Mosig, Fahd Azzabi Zouraq, Kai Johnsson, Yann Barrandon, Ariane Rochat, Thomas Michael Braschler, Johannes Alexander Mosig, Jean-Baptiste Bureau

ELSEVIER SCIENCE INC2023

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

Kai Johnsson

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 ...

NATURE PORTFOLIO2023

Exchangeable HaloTag Ligands for Super-Resolution Fluorescence Microscopy

Kai Johnsson, Michelle Susanne Frei

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 ...

AMER CHEMICAL SOC2023

Fluorescent and Bioluminescent Calcium Indicators with Tuneable Colors and Affinities

Kai Johnsson

We introduce a family of bright, rhodamine-based calcium indicators with tuneable affinities and colors. The indicators can be specifically localized to different cellular compartments and are compatible with both fluorescence and bioluminescence readouts ...

AMER CHEMICAL SOC2022

Live-Cell Fluorescence Lifetime Multiplexing Using Synthetic Fluorescent Probes

Kai Johnsson

Fluorescence lifetime multiplexing requires fluorescent probes with distinct fluorescence lifetimes but similar spectral properties. Even though synthetic probes for many cellular targets are available for multicolor live-cell fluorescence microscopy, few ...

AMER CHEMICAL SOC2022

Engineered HaloTag variants for fluorescence lifetime multiplexing

Kai Johnsson, Michelle Susanne Frei

HaloTag variants offer distinct brightness and fluorescence lifetimes compared with HaloTag7 when labeled with rhodamines. These variants were used for multiplexed imaging with a single fluorophore and to create lifetime-based cell cycle indicators. ...

NATURE PORTFOLIO2022

Synergizing Exchangeable Fluorophore Labels for Multitarget STED Microscopy

Kai Johnsson

Investigating the interplay of cellular proteins with optical microscopy requires multitarget labeling. Spectral multiplexing using high-affinity or covalent labels is limited in the number of fluorophores that can be discriminated in a single imaging expe ...

AMER CHEMICAL SOC2022

A synergistic strategy to develop photostable and bright dyes with long Stokes shift for nanoscopy

Kai Johnsson

The quality and application of super-resolution fluorescence imaging greatly lie in the dyes' properties, including photostability, brightness, and Stokes shift. Here we report a synergistic strategy to simultaneously improve such properties of regular flu ...

Nature Portfolio2022