Publications by Kai Johnsson | EPFL Graph Search

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We report the semisynthesis of a fluorescent glutamate sensor protein on cell surfaces. Sensor excitation at 547 nm yields a glutamate-dependent emission spectrum between 550 and 700 nm that can be exploited for ratiometric sensing. On cells, the sensor di ...

The invention concerns a combinatorial method for the generation of new split-protein sensors, and its application towards the (beta/alpha)8-barrel enzyme N-(5'-phosphoribosyl)-anthranilate isomerase Trp1p from Saccharomyces cerevisiae is demonstrated. The ...

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 ...

The present invention relates to methods of transferring a label from suitable substrates to O6-alkylguanine-DNA alkyltransferase (AGT) fusion proteins, to suitable fusion proteins, to suitable variants of AGT, and to novel labelled fusion proteins obtained. A protein of interest is incorporated into an AGT fusion protein, the AGT fusion protein is contacted with an AGT substrate carrying a label, and the AGT fusion protein is detected and/or manipulated using the label in a system designed for recognising

The invention relates to the detection of the cofactor reduced nicotinamide adenine dinucleotide phosphate (NADPH). Provided is a sensor molecule for the resonance energy transfer (RET)-based detection of NADPH, the sensor comprising a segment A connected ...

A fluorogenic probe for plasma membrane proteins based on the dye Nile Red and SNAP-tag is introduced. It takes advantage of Nile Red, a solvatochromic molecule highly fluorescent in an apolar environment, such as cellular membranes, but almost dark in a p ...

Benzothiazinones (BTZs) form a new class of potent antimycobacterial agents. Although the target of BTZs has been identified as decaprenylphosphoryl-β-D-ribose 2'-epimerase (DprE1), their detailed mechanism of action remains obscure. Here we demonstrate that BTZs are activated in the bacterium by reduction of an essential nitro group to a nitroso derivative, which then specifically reacts with a cysteine residue in the active site of DprE1.

A review with 16 refs. on the mechanism of action of isoniazid, the worldwide known drug against tuberculosis. [on SciFinder (R)]

A series of mutants bearing single amino acid substitutions often encountered in the catalase/peroxidase, KatG, from isoniazid-resistant isolates of Mycobacterium tuberculosis has been produced by site-directed mutagenesis. The resultant enzymes were overexpressed, purified and characterized. Replacing Cys-20 by Ser abolished disulphide-bridge formation, but did not affect either dimerization of the enzyme or catalysis. The substitution of Thr-275, which is probably involved in electron transfer from the ha

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 ...

The invention concerns the introduction of a coupling group to 6-O-Alkylguanine DNA alkyltransferase from a 6-O-Alkylguanine-coupling group deriv. that enables the immobilization of the enzyme for subsequent anal. The coupling group is bound covalently to the enzyme; the immobilization to the surface is either by covalent or non-covalent binding. The coupling group can be biotin; the 6-O-Alkylguanine DNA alkyltransferase-biotin is immobilized to streptavidin coated surface. Independently from the coupling g

For decades chemists have focused on increasing the brightness of fluorophores. In super-resolution microscopy, however, fluorophores that preferentially exist in a non-fluorescent state, but occasionally re-arrange into a fluorescent form, can give better results.

The invention provides a method of crosslinking two objects of interest, comprising the steps of : i) providing a fusion protein comprising at least a first protein and a second protein, wherein both the first and the second protein are, based on their str ...

The authors present here a novel approach to induce protein dimerization in living cells through covalent labeling of fusion proteins with ligands which are interacting with other proteins. The covalent labeling is based on the reaction of the DNA repair protein O6-alkylguanine-DNA alkyltransferase with O6-benzylguanine coupled to an appropriate ligand. Using methotrexate as a ligand, it is shown that the approach can be used to control transcription in the yeast Saccharomyces cerevisiae. The specificity of

It is difficult to develop suitable fluorescent probes for live-cell nanoscopy, but a general strategy is now reported that can transform regular fluorophores into fluorogenic probes with excellent cell permeability and low unspecific background signals. U ...

Biosensors are used in many fields to measure the concentration of analytes, both in a cellular context and in human samples for medical care. Here, we outline the design of two types of modular biosensors: SNAP-tag-based indicators with a Fluorescent Intramolecular Tether (SNIFITs) and LUCiferase-based Indicators of Drugs (LUCIDs). These semisynthetic biosensors quantitatively measure analyte concentrations in vitro and on cell surfaces by an intramolecular competitive mechanism. We provide an overview of

We introduce luciferases whose emission maxima can be tuned to different wavelengths by chemical labeling. These tunable luciferases are generated by inserting the small luciferase NanoLuc into the structures of the self-labeling proteins SNAP-tag or HaloT ...

Obtaining patient-specific information through the quantification of small molecules and proteins in bodily fluids is essential for personalized therapies. Point-of-care (POC) diagnostic devices hold the promise of delivering such benefit to a wide range o ...

We describe the synthesis and fluorescence properties of a Fura-2FF-based fluorescent Ca(2+) indicator that can be covalently linked to SNAP-tag fusion proteins and retains its Ca(2+) sensing ability after coupling to protein.

Kai Johnsson

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A Semisynthetic Fluorescent Sensor Protein for Glutamate

Method for identification of suitable fragmentation sites in a reporter protein

Fluorescent and Bioluminescent Calcium Indicators with Tuneable Colors and Affinities

Protein labelling with o6-alkylguanine-dna alkyltransferase

Identification of a small molecule with activity against drug-resistant and persistent tuberculosis (vol 110, pg E2510, 2013)

Sensors, methods and kits for detecting nadph based on resonance energy transfer

A fluorogenic probe for SNAP-tagged plasma membrane proteins based on the solvatochromic molecule Nile Red

Benzothiazinones: prodrugs that covalently modify the decaprenylphosphoryl-β-D-ribose 2'-epimerase DprE1 of Mycobacterium tuberculosis

Spontaneous formation of the bioactive form of the tuberculosis drug isoniazid

Use of site-directed mutagenesis to probe the structure, function and isoniazid activation of the catalase/peroxidase, KatG, from Mycobacterium tuberculosis

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

Selective immobilization of active 6-O-Alkylguanine DNA alkyltransferase for its determination by transferring a coupling group to the enzyme from a 6-O-Alkylguanine derivative

FLUORESCENCE MICROSCOPY Strategic blinking

Method of crosslinking two objects of interest

Induced Protein Dimerization in Vivo through Covalent Labeling

A general strategy to develop cell permeable and fluorogenic probes for multicolour nanoscopy

Rational Design and Applications of Semisynthetic Modular Biosensors: SNIFITs and LUCIDs

Luciferases with tunable emission wavelengths

Highly Modular Bioluminescent Sensors for Small Molecules and Proteins

Fura-2FF-based calcium indicator for protein labeling