Publications by Kai Johnsson | EPFL Graph Search

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The identification of all protein targets of a given drug or bioactive molecule within the human body is a prerequisite for an understanding of its beneficial and deleterious activities. Current approaches to reveal protein targets often fail to reveal phy ...

A general method for covalent labeling of fusion proteins in vivo that complements the existing methods for protein labeling in vivo and in vitro is presented. This new method might lead to new ways of studying and manipulating proteins in living cells. Covalent attachment of the small mol. to the fusion protein is achieved by the unusual mechanism of the human DNA repair protein O6-alkylguanine-DNA alkyltransferase, which irreversibly transfers the alkyl group from its substrate, O6-alkylguanine-DNA, to on

A review with 15 refs. Directed mol. evolution of enzymes and proteins has emerged as an extremely powerful method to create proteins with novel properties, both for practical applications as well as for mechanistic studies. To demonstrate the underlying principles of this approach, the authors describe here their work on the heme-contg. cytochrome c peroxidase (I) from Saccharomyces cerevisiae. Using directed evolution, the authors changed the substrate specificity of I from the protein, cytochrome c, to a

The past 20 years have witnessed the advent of numerous technologies to specifically and covalently label proteins in cellulo and in vivo with synthetic probes. These technologies range from self-labeling proteins tags to non-natural amino acids, and the q ...

A review. Directed evolution consists of repetitive cycles of random mutagenesis of the protein/peptide sequence followed by screening or selection of candidates with desired properties. Many different approaches are used to introduce mutations into a gene; most of the currently used are error-prone polymerase chain reaction (PCR), DNA shuffling, and satn. mutagenesis. On the other hand, the techniques used in screening or selection expts. range from facile colony activity screening to yeast two-hybrid syst

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 ...

A review with 100 refs. The enormous potential of combinatorial approaches for studying problems in biol. and chem. has been clearly demonstrated over the last several years. In particular, phage display has become one of the major techniques for the use of combinatorial peptide and protein libraries. The reasons for the success of phage display are, at least, threefold: (1) phage display of combinatorial libraries creates a direct link between phenotype (the selectable properties of interest from the displ

Studying proteins in living cells generally requires the construction of a fusion protein between the protein of interest and an appropriate tag. Currently used fusion protein-based assays rely on the genetically encoded properties of the tag, which significantly limits their scope of applications. Here we present a general method for the in vivo labeling of fusion proteins with small mols. possessing functionalities that can not be genetically encoded. The specific attachment of the small mol. to the fusio

Cholera toxin enters cells via an unusual pathway that involves trafficking through endosomes to the endoplasmic reticulum (ER). Whether the toxin induces its own pathway or travels along a physiological retrograde route is not known. To study its traffick ...

The specific and covalent labeling of fusion proteins with synthetic mols. opens up new ways to study protein function in the living cell. Here the authors present a novel method that allows for the specific and exclusive extracellular labeling of proteins on the surfaces of live cells with a large variety of synthetic mols. including fluorophores, protein ligands, or quantum dots. The approach is based on the specific labeling of fusion proteins of acyl carrier protein with synthetic mols. through post-tra

For many drugs, finding the balance between efficacy and toxicity requires monitoring their concentrations in the patient's blood. Quantifying drug levels at the bedside or at home would have advantages in terms of therapeutic outcome and convenience, but current techniques require the setting of a diagnostic laboratory. We have developed semisynthetic bioluminescent sensors that permit precise measurements of drug concentrations in patient samples by spotting minimal volumes on paper and recording the sign

Acetylcholine is a key neurotransmitter, and anticholinesterase agents are essential compounds used as medical drugs, pesticides, and chemical warfare agents. A semisynthetic fluorescence-based probe for the direct, real-time detection of acetylcholine and ...

Monitoring metabolites at the point of care could improve the diagnosis and management of numerous diseases. Yet for most metabolites, such assays are not available. We introduce semisynthetic, light-emitting sensor proteins for use in paper-based metaboli ...

The design and synthesis of chem. probes to study and to elucidate complex biol. problems is becoming an increasingly important field in chem. We are interested in the repair of O6-alkylated guanines in DNA, a DNA lesion that results from alkylation by S-adenosylmethionine or exogenous toxins and which has been shown to be highly mutagenic and carcinogenic. The DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT; EC 2.1.1.63) reverses this alkylation by transferring the alkyl group to a reactive cy

Elucidating the role of metal ion homeostasis in physiological and pathological processes requires detection tools with high sensitivity and selectivity, spectral versatility, and precise subcellular localization. Here, we introduce a modular strategy for generating fluorescent metal ion indicators which are comprised of a sulfonamide-functionalized chelator, a rhodamine derivative and a ligand for bioconjugation to self-labeling proteins. With a concise three-step synthesis, the design allows tuning of bot

The emerging technique termed functional identification of target by expression proteomics (FITExP) has been shown to identify the key protein targets of anti-cancer drugs. Here, we use this approach to elucidate the proteins involved in the mechanism of a ...

Imaging actin‐dependent processes in live cells is important for understanding numerous biological processes. However, currently used natural‐product‐based fluorescent probes for actin filaments affect the dynamics of actin polymerization and can induce undesired cellular phenotypes. Here, we introduce SiR‐XActin, a simplified jasplakinolide‐based, far‐red fluorescent probe that enables bright and photostable staining in various cell types without requiring genetic modifications. Due to its relatively weak

Previous models of protein p36 based on proteolytic fragments describe the tail and core as 2 noninteracting domains. However, monoclonal antibody H28 recognized a discontinuous epitope, which covers the peptide segments around serine-25 in the tail and around glutamate-65 in the core of porcine p36. Thus, the phosphorylatable tyrosine-23 is much closer to the 1st consensus sequence (residues 46-62) of Ca2+/lipid-binding proteins than previously thought. This apposition is in line with biochem. expts. indic

The invention relates to compositions comprising sulfasalazine or sulfapyridine and products of a biosynthetic pathway that requires tetrahydrobiopterin. Such compositions are useful for the treatment of inflammatory bowel diseases or rheumatoid arthritis, ...

Characterizing the movement, interactions, and chem. microenvironment of a protein inside the living cell is crucial to a detailed understanding of its function. Most strategies aimed at realizing this objective are based on genetically fusing the protein of interest to a reporter protein that monitors changes in the environment of the coupled protein. Examples include fusions with fluorescent proteins, the yeast two-hybrid system, and split ubiquitin. However, these techniques have various limitations, and

Kai Johnsson

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Searching for the Protein Targets of Bioactive Molecules

Labeling of fusion proteins with small molecular in vivo

Evolutionary approaches to study cytochrome c peroxidase

Imaging and manipulating proteins in live cells through covalent labeling

Exploring the Capabilities of Nucleic Acid Polymerases by Use of Directed Evolution

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

Phage display of combinatorial peptide and protein libraries and their applications in biology and chemistry

Protein chemistry in living cells

Investigating Endocytic Pathways to the Endoplasmic Reticulum and to the Cytosol Using SNAP-Trap

Specific Labeling of Cell Surface Proteins with Chemically Diverse Compounds

Bioluminescent sensor proteins for point-of-care therapeutic drug monitoring

Sensing Acetylcholine and Anticholinesterase Compounds

Semisynthetic sensor proteins enable metabolic assays at the point of care

Synthesis and applications of chemical probes for human O6-alkylguanine-DNA alkyltransferase

Localizable fluorescent metal ion indicators with tunable colors

Expression proteomics study to determine metallodrug targets and optimal drug combinations

SiR‐XActin: A Fluorescent Probe for Imaging Actin Dynamics in Live Cells

A discontinuous epitope on p36, the major substrate of src tyrosine-protein-kinase, brings the phosphorylation site into the neighborhood of a consensus sequence for calcium/lipid-binding proteins

Compositions and use of sulfasalazine

A general method for the covalent labeling of fusion proteins with small molecules in vivo