Identification of protein binding partners of small molecules using label-free methods.

Introduction: Drug discovery efforts across the globe are chasing new drug targets and novel mechanisms of action. To support the identification of novel mechanisms of action, phenotype-based drug screening has significantly increased over the last decade. Along with the rise in phenotypic screening, methods and technologies that can help to identify drug targets of phenotypically screened 'hits' have also evolved significantly.

Dynamics and mechanism of DNA repair in a biomimetic system: flavin-thymine dimer adduct.

To mimic photolyase for efficient repair of UV-damaged DNA, numerous biomimetic systems have been synthesized, but all show low repair efficiency. The molecular mechanism of this low-efficiency process is still poorly understood. Here we report our direct mapping of the repair processes of a flavin-thymine dimer adduct with femtosecond resolution.

Affinity-based chemoproteomics with small molecule-peptide conjugates.

In affinity-based chemoproteomics strategies, the direct immobilization of small bioactive probe molecules to a solid support may pose problems with respect to the preservation of the functional activity toward the target proteins. Typically, immobilized molecules on solid supports exhibit lower affinity for target proteins compared to the free parent molecule. This may lead to a failure to specifically capture the target proteins or to unacceptable losses during the washing steps.

Ultrafast solvation dynamics at binding and active sites of photolyases.

Dynamic solvation at binding and active sites is critical to protein recognition and enzyme catalysis. We report here the complete characterization of ultrafast solvation dynamics at the recognition site of photoantenna molecule and at the active site of cofactor/substrate in enzyme photolyase by examining femtosecond-resolved fluorescence dynamics and the entire emission spectra. With direct use of intrinsic antenna and cofactor chromophores, we observed the local environment relaxation on the time scales from a few picoseconds to nearly a nanosecond.

Small-molecule affinity chromatography coupled mass spectrometry for drug target deconvolution.

Background: Current drug discovery organizations have renewed interest in phenotypic/function based screening for the identification of novel small-molecule drug candidates. Phenotypic screening faces the challenge of deconvoluting the identity of molecular targets of small-molecules through which they exert their biological effect. The identity of the target is crucial for understanding the mechanism of drug action, rational drug design, interpretation of any toxicological findings and patient stratification.

Capture of drug targets from live cells using a multipurpose immuno-chemo-proteomics tool.

Recently we have described the development of an Immuno-chemo-proteomics method for drug target deconvolution and profiling the toxicity of known drugs ( Saxena , C. ; Zhen , E. ; Higgs , R.

Ultrafast dynamics of flavins in five redox states.

We report here our systematic studies of excited-state dynamics of two common flavin molecules, FMN and FAD, in five redox states--oxidized form, neutral and anionic semiquinones, and neutral and anionic fully reduced hydroquinones--in solution and in inert protein environments with femtosecond resolution. Using protein environments, we were able to stabilize two semiquinone radicals and thus observed their weak emission spectra. Significantly, we observed a strong correlation between their excited-state dynamics and the planarity of their flavin isoalloxazine ring.

An immuno-chemo-proteomics method for drug target deconvolution.

Chemical proteomics is an emerging technique for drug target deconvolution and profiling the toxicity of known drugs. With the use of this technique, the specificity of a small molecule inhibitor toward its potential targets can be characterized and information thus obtained can be used in optimizing lead compounds. Most commonly, small molecules are immobilized on solid supports and used as affinity chromatography resins to bind targets.

Femtochemistry in enzyme catalysis: DNA photolyase.

Photolyase uses light energy to split UV-induced cyclobutane pyrimidine dimers in damaged DNA. This photoenzyme encompasses a series of elementary dynamical processes during repair function from early photoinitiation by a photoantenna molecule to enhance repair efficiency, to in vitro photoreduction through aromatic residues to reconvert the cofactor to the active form, and to final photorepair to fix damaged DNA. The corresponding series of dynamics include resonance energy transfer, intraprotein electron transfer, and intermolecular electron transfer, bond breaking-making rearrangements and back electron return, respectively.

Femtosecond dynamics of flavin cofactor in DNA photolyase: radical reduction, local solvation, and charge recombination.

We report here our femtosecond studies of the photoreduction dynamics of the neutral radical flavin (FADH) cofactor in E. coli photolyase, a process converting the inactive form to the biologically active one, a fully reduced deprotonated flavin FADH(-). The observed temporal absorption evolution revealed two initial electron-transfer reactions, occurring in 11 and 42 ps with the neighboring aromatic residues of W382 and F366, respectively.

Direct observation of thymine dimer repair in DNA by photolyase.

Photolyase uses light energy to split UV-induced cyclobutane dimers in damaged DNA, but its molecular mechanism has never been directly revealed. Here, we report the direct mapping of catalytic processes through femtosecond synchronization of the enzymatic dynamics with the repair function. We observed direct electron transfer from the excited flavin cofactor to the dimer in 170 ps and back electron transfer from the repaired thymines in 560 ps.

Ultrafast dynamics of resonance energy transfer in cryptochrome.

In this communication, we report the ultrafast dynamics of resonance energy transfer in a blue-light photoreceptor, Vibrio cholerae cryptochrome. The transfer was observed to occur in 60 ps. We also studied the local rigidity and solvation around the binding site of the photoantenna molecule.