Site-selective protein modification via disulfide rebridging for fast tetrazine/trans-cyclooctene bioconjugation

An inverse electron demand Diels–Alder reaction between tetrazine and trans-cyclooctene (TCO) holds great promise for protein modification and manipulation. Herein, we report the design and synthesis of a tetrazine-based disulfide rebridging reagent, which allows the site-selective installation of a tetrazine group into disulfide-containing peptides and proteins such as the hormone somatostatin (SST) and the antigen binding fragment (Fab) of human immunoglobulin G (IgG). The fast and efficient conjugation of the tetrazine modified proteins with three different TCO-containing substrates to form a set of bioconjugates in a site-selective manner was successfully demonstrated for the first time. Homogeneous, well-defined bioconjugates were obtained underlining the great potential of our method for fast bioconjugation in emerging protein therapeutics. The formed bioconjugates were stable against glutathione and in serum, and they maintained their secondary structure. With this work, we broaden the scope of tetrazine chemistry for site-selective protein modification to prepare well-defined SST and Fab conjugates with preserved structures and good stability under biologically relevant conditions

Comet-assay parameters as rapid biomarkers of exposure to dietary/environmental compounds - An in vitro feasibility study on spermatozoa and lymphocytes

Twelve chemical compounds have been selected for the European NewGeneris study on the basis of their potential to damage DNA, in order to establish adequate and reliable biomarkers of exposure. These genotoxic chemicals include heterocyclic amines, organochlorines, polycyclic aromatic hydrocarbons, mycotoxins, lipid peroxidation products and alcohol. Damage in somatic cells such as lymphocytes could give rise to cancer, while damage in germ cells could not only give rise to cancer but also to heritable defects. The alkaline Comet assay, with and without metabolic activation, as well as the neutral Comet assay were used to assess DNA integrity in spermatozoa and lymphocytes after in vitro treatment with low, middle and high doses of each chemical. DNA-reactive aldehydes generated by lipid peroxidation, food mutagens such as heterocyclic amines, nitrosamine and benzo[a]pyrene produced the highest amounts of DNA damage, even without metabolic activation. Damage seen with the neutral Comet assay – detecting primarily double-strand breaks – was lower than with the alkaline assay. In general, there was increased damage in the spermatozoa by comparison with the lymphocytes, with altered slopes in the dose–response curves. The Comet assay with sperm was generally very sensitive in assessing genotoxic damage, with the Comet parameters being good biomarkers of induced DNA damage. Establishing reliable biomarkers of exposure for the evaluation of dietary/environmental carcinogens is of utmost importance to protect our health and the health of our offspring

2-Hydr­oxy-5-nitro­benzaldehyde 2,4-dinitro­phenyl­hydrazone

In the title compound, C13H9N5O7, one of the nitro groups is twisted away from the attached benzene ring by 16.21 (8)°. The dihedral angle between the two benzene rings is 4.63 (1)°. The mol­ecular structure is stabilized by intra­molecular N—H⋯O and O—H⋯N hydrogen bonds which generate an S(6) ring motif. The mol­ecules pack as layers parallel to the ab plane; mol­ecules of adjacent layers are linked into chains along the [101] direction through N—H⋯O hydrogen bonds

Fingerprinting of hydroxyl radical-attacked polysaccharides by N-isopropyl-2-aminoacridone labelling

Hydroxyl radicals ((•)OH) cause non-enzymic scission of polysaccharides in diverse biological systems. Such reactions can be detrimental (e.g. causing rheumatic and arthritic diseases in mammals) or beneficial (e.g. promoting the softening of ripening fruit, and biomass saccharification). Here we present a method for documenting (•)OH action, based on fluorescent labelling of the oxo groups that are introduced as glycosulose residues when (•)OH attacks polysaccharides. The method was tested on several polysaccharides, especially pectin, after treatment with Fenton reagents. 2-Aminoacridone plus cyanoborohydride reductively aminated the oxo groups in treated polysaccharides; the product was then reacted with acetone plus cyanoborohydride, forming a stable tertiary amine with the carbohydrate linked to N-isopropyl-2-aminoacridone (pAMAC). Digestion of labelled pectin with ‘Driselase’ yielded several fluorescent products which on electrophoresis and HPLC provided a useful ‘fingerprint’ indicating (•)OH attack. The most diagnostic product was a disaccharide conjugate of the type pAMAC·UA-GalA (UA=unspecified uronic acid), whose UA-GalA bond was Driselase-resistant (product 2A). 2A was clearly distinguishable from GalA-GalA–pAMAC (disaccharide labelled at its reducing end), which was digestible to GalA–pAMAC. The methodology is applicable, with appropriate enzymes in place of Driselase, for detecting natural and artificial (•)OH attack in diverse plant, animal and microbial polysaccharides