Protein reactivity

Figure 19.1 A schematic view of the common formaldehyde-induced modifications in proteins. Reactive methylol adducts are formed in the initial reaction between formaldehyde and cysteine or the amino groups of basic amino acid residues. The methylol adduct can subsequently undergo a dehydration reaction to form a Schiff s base. Adducted residues can undergo a second reaction to form methylene bridges or can convert to the ethoxymethyl adduct after the ethanol dehydration step.

For effective sensitization, a chemical must therefore be inherently protein-reactive or must be converted in the skin to a protein-reactive metabolite. Chemicals that are unable to associate effectively with proteins will fail to stimulate a cutaneous immune response. For those chemical contact allergens that require metabolism to a protein reactive species, it is possible that genetic differences in metabolism may play a role in the differential susceptibility of individuals to the development of contact hypersensitivity responses to these materials. 

Although in the past biotransformation to produce protein-reactive products has not been considered important in discovery toxicology studies, this situation appears to be changing. The limiting factor has been availability of radiolabeled drug to conduct appropriate covalent binding studies, but strategies have been proposed to overcome this obstacle [25],... 

Boelsterli UA. Xenobiotic acyl glucuronides and acyl CoA thioesters as protein-reactive metabolites with the potential to cause idiosyncratic drug reactions. Curr Drug Metab 2002 3(4) 439-450. 

As mentioned earlier, the response of each protein will vary. This is especially apparent with colorimetric assays or derivatization methods requiring a chemical reaction. These protein-to-protein reactivity differences mean that a protein assay suitable for one protein may not be suitable for another. Even for a given protein and a specific protein determination method, results may still vary based on limitations of the assay. Methods requiring extensive sample preparation including protein concentration, buffer exchange, and time-sensitive reactions are liable to be less reproducible than direct measurement techniques, which have fewer variable parameters. The application will determine the suitability of the method. 

Jiang H, Curran S, Ruiz-Vazquez E, Liang B, Winchester R, Chess L Regulatory CDS + T cells fine-tune the myelin basic protein-reactive T cell receptor V(5 repertoire during experimental autoimmune encephalomyelitis. Proc Natl Acad Sci USA 2003 100 8378-8383. 

Sulphonamide antimicrobial agents (Figure 8.22) such as sulphamethoxazole [21] are oxidized to protein-reactive cytotoxic metabolites in the liver and also other tissues. These include hydroxylamines and further products such as nitroso-deriva-tives. Sulphonamide drugs are linked with agranulocytosis, aplastic anaemia and... 

We have discovered a novel protein immobilization method, i.e., a Three-Dimensional Nanostructured Protein Hydrogel (3-D NPH), which is composed of protein-reactive polymer hybrid nanoparticles to detect protein-protein interactions. The 3-D NPH can be easily prepared by spotting a protein/reactive polymer mixture on a substrate. The resulting 3-D NPH is characterized by large amounts of immobilized proteins and a novel porous structure. 

Clozapine is principally metabolized to N -desmethylclozapine (norclozapine). It is also metabolized to and n-oxide, other hydroxyl metabolites, and a protein-reactive metabolite. The n-oxide can be converted back to clozapine. The enzyme responsible for the metabolism of clozapine to norclozapine is the cytochrome P450 1A2 enzyme (325). This is consistent with a study showing that caffeine, a marker for 1A2, is cleared in relationship to the conversion of clozapine to norclozapine ( 326). Discontinuation of coffee intake can decrease the clozapine plasma levels by more than 50%, and increasing caffeine intake can produce a reemergence of the side effects (e.g., drowsiness, excess salivation). Additionally, smoking, which induces 1A2, lowers clozapine plasma levels. Fluvoxamine, an inhibitor of 1A2, dramatically increases plasma levels, and on occasion, adverse effects are seen ( 327). This phenomenon can lead to clozapine intoxication in patients on high doses of fluvoxamine. 

Eosinophils Weakly phagocytic, secrete cationic proteins, reactive reduced oxygen species, leukotrienes, prostaglandins, cytokinins... 

Niman, H L., Houghten, R A., Walker, L E., Reisfeld, R A., Wilson, I. A, Hogle, J. M., and Lemer, R, A. (1983) Generation of protein-reactive antibodies by short peptides is an event of high frequency implications for the structural basis of immune recognition Proc Natl Acad Sci USA 80,4949-4953... 

Although present in several approved drugs, protein reactive chemical groups are known to produce screening artefacts and are undesirable starting points for F2L optimization.1461 We eliminated potentially protein reactive chemical groups, such as aldehydes, phosphon-ate esters and activated ketones, in order to avoid identification of covalent, irreversible fragment binders. Furthermore, we also removed potential toxicophores. 

B30. Burns, J., Rosenzweig, A., Zweiman, B., and Lisak, R. R, Isolation of myelin basic protein-reactive T cell lines from normal human blood. Cell. Immunol. 81, 435-440 (1993). 

Drahl C, Cravatt BF, Sorensen EJ (2005) Protein-reactive natural products. Angew Chem Int... 

This chapter discusses several case studies of successful ABPP approaches in annotating the target proteins of natural products. The examples are classified according to the nature of the protein-reactive electrophilic group within the natural products. This article builds on the recent excellent review by Sieber et al. [22],... 

Kunzmann MH, Straub I, Bottcher T, Sieber SA (2011) Protein reactivity of natural product-derived y-butyrolactones. Biochemistry 50 910-916... 

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