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Kai Johnsson

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Related publications (125)

Photobleaching-free infrared near-field microscopy localizes molecules in neurons

Giorgio Margaritondo, Kai Johnsson, Harald Hirling, Michel Kropf, Johanna Generosi

High-resolution detection of specific molecules in cells is a major challenge in biology. We show that infrared scanning near-field microscopy can detect the spatial distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid–type glutamate r ...

2008

An engineered protein tag for multi-protein labeling in living cells

Kai Johnsson, Alexandre Juillerat, Christian Heinis

The visualization of complex cellular processes involving multiple proteins requires the use of spectroscopically distinguishable fluorescent reporters. We have previously introduced the SNAP-tag as a general tool for the specific labeling of SNAP-tag fusi ...

2008

AMPA receptor imaging by infrared scanning near-field optical microscopy

Giorgio Margaritondo, Kai Johnsson, Harald Hirling, Michel Kropf, Johanna Generosi

Infrared scanning near-field optical microscopy is used to detect AMPA-type glutamate receptor clusters in hippocampal neuron cells. AMPA's GluR2-subunits were marked with the fluorophore Alexa488 and high-resolution micrographs were taken at 6.25 µm wavel ...

Wiley2008

A Covalent Chemical Genotype-Phenotype Linkage for in vitro Protein Evolution

Kai Johnsson, India Christina Sielaff

2007

Chemical probes shed light on fusion proteins

Kai Johnsson

Site-specific protein labeling with synthetic dyes is an emerging technique for live cell imaging. A protein or peptide tag fused to the protein of interest provides the means for attachment of a fluorophore or other small molecule probe, to allow non-inva ...

2007

Inducing and sensing protein-protein interactions in living cells via selective crosslinking

Kai Johnsson

2007

Chemical tools for biomolecular imaging

Kai Johnsson

2007

Specific substrates for O6- alkylguanine-DNA alkyltransferase

Kai Johnsson, India Christina Sielaff

The invention relates to substrates for O-alkylguanine-DNA alkyltransferases (AGT) of formula R1-A-X-CH2-R3-R4-L1, wherein A is a group recognized by AGT as a substrate, X is oxygen or sulfur, R1 is a group -R2-L2 or a group R5, R2 and R4 are, independe ...

2006

Chimeric streptavidins with reduced valencies

Kai Johnsson

2006

Mutants of o6-alkylguanine-dna alkyltransferase

Kai Johnsson, Christopher Chidley, Antje Keppler, Alexandre Juillerat, Thomas Gronemeyer, Christian Heinis

The invention relates to AGT mutants showing, when compared to the wild type human AGT, two or more advantageous properties selected from (a) reduced DNA interaction (b) localisation of the expressed protein in eukaryotic cells that is no longer restricted ...

2006

Protein function microarrays based on self-immobilizing and self-labeling fusion proteins

Kai Johnsson, India Christina Sielaff, Harm-Anton Klok, Anke Arnold, Stefano Tugulu

Protein microarrays are an attractive approach for the high-throughput analysis of protein function, but their impact on proteomics has been limited by the technical difficulties associated with their generation. Here we demonstrate that fusion proteins of ...

2006

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

Rudolf Hovius, Horst Vogel, Jean-Manuel Segura, Kai Johnsson, Nathalie George

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 ...

National Academy of Sciences2006

Posttranslational covalent labeling reveals heterogeneous mobility of individual G protein-coupled receptors in living cells

Horst Vogel, Jean-Manuel Segura, Kai Johnsson, Bruno Meyer, Raphael Franzini, Nathalie George

2006

Evolving the substrate specificity of O6-alkylguanine-DNA alkyltransferase through loop insertion for applications in molecular imaging

Kai Johnsson, Christian Heinis, Simone Schmitt

2006

Directed evolution of O6-alkylguanine-DNA alkyltransferase for applications in protein labeling

Kai Johnsson, Christopher Chidley, Alexandre Juillerat, Thomas Gronemeyer, Christian Heinis

The specific reaction of O6-alkylguanine-DNA alkyltransferase (AGT) with O6-benzylguanine (BG) derivatives allows for a specific labeling of AGT fusion proteins with chemically diverse compounds in living cells and in vitro. The efficiency of the labeling ...

Oxford University Press2006

Covalent labeling of cell-surface proteins for in-vivo FRET studies

Rudolf Hovius, Horst Vogel, Jean-Manuel Segura, Kai Johnsson, Bruno Meyer, Nathalie George, Pedro Pascoal

Fluorescence resonance energy transfer (FRET) is a powerful technique to reveal interactions between membrane proteins in live cells. Fluorescence labeling for FRET is typically performed by fusion with fluorescent proteins (FP) with the drawbacks of a lim ...

2006

The Laboratory in a Droplet

Kai Johnsson

In this issue of Chem. & Biol., the groups of Tawfik and Griffiths present fluorescence-activated cell sorting of double emulsions as a generally applicable screen for enzyme activity. This novel methodol. increases the throughput of a typical enzyme scree ...

2005

Fast directed evolution of non-immunoglobulin proteins by somatic hypermutation in immune cells

Kai Johnsson, Christian Heinis

A review. New, improved phenotypes. Somatic hypermutation in immune cells can be used for the fast directed evolution of proteins other than Igs (e.g., autofluorescent proteins). The target gene is inserted into the genome of activated B lymphocytes where ...

2005

Engineering substrate specificity of O6-alkylguanine-DNA alkyltransferase for specific protein labeling in living cells

Hugues Jaccard, Kai Johnsson, Alexandre Juillerat, India Christina Sielaff, Béatrice Kunz, Christian Heinis

Fusion proteins of human O6-alkylguanine-DNA alkyltransferase (AGT) can be specifically labeled with a wide variety of synthetic probes in mammalian cells; this makes them an attractive tool for studying protein function. However, to avoid undesired labeli ...

2005

Protein-functionalized polymer brushes

Kai Johnsson, India Christina Sielaff, Harm-Anton Klok, Anke Arnold, Stefano Tugulu

Understanding and controlling the interactions between synthetic and biol. materials is of great importance for the development of novel materials for a variety of biomedical and bioanal. applications, including for example stents, vascular grafts and prot ...

2005

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