Enzymatic deglutathionylation to generate interleukin-4 cysteine muteins with free thiol

Interleukin-4 (IL-4) is a prototypical regulator protein of the immune system that is crucial for the pathogenesis and maintenance of asthma and other atopic diseases. It, together with IL-13, uses the IL-4 receptor α chain (IL-4Rα) to signal into immune and other cells. An IL-4 mutein acting as a dual IL-4/IL-13 receptor antagonist is in clinical development. Here, it is described how IL-4 muteins containing a single engineered cysteine with a free thiol can be prepared and used for site-specific chemical modification. The muteins were initially expressed in E. coli, refolded, and purified, but not in a fully reduced nonconjugated form. Attempts to reduce the cysteine chemically failed because the native disulfide bonds of IL-4 were also reduced under similar conditions. Therefore, an enzymatic procedure was developed to reduce glutathionylated IL-4 cysteine muteins employing glutaredoxin and reduced glutathione. Cysteine muteins engineered at four different positions around the IL-4Rα binding site were enzymatically reduced at different rates. All muteins were prepared with free thiol in reasonable yield and were modified by N-ethylmaleimide (NEM) or maleimido-PEG. The effect on IL-4Rα binding of cysteine substitution and of the site-specific modification by glutathione, N-ethylmaleimide (NEM), or a branched 2.36 kDa poly(ethylene glycol) (PEG) will be discussed.     

Increasing peptide identifications and decreasing search times for ETD spectra by pre-processing and calculation of parent precursor charge

Background

Early diagnosis and treatment of Mycobacterium tuberculosis infection can prevent most deaths resulting from this pathogen; however, multidrug-resistant strains present serious threats to global tuberculosis control and prevention efforts. In this study, we identified antigens that could be used for the serodiagnosis of drug-resistant M. tuberculosis strains, using a proteomics-based analysis.

Results

Serum from patients infected with drug-resistant or drug-susceptible M. tuberculosis strains and healthy controls was subjected to two-dimensional gel electrophoresis using a western blot approach. This procedure identified nine immunoreactive proteins, which were subjected to MALDI-TOF-MS analysis. Six recombinant proteins, namely rRv2031c, rRv0444c, rRv2145c, rRv3692, rRv0859c, and rRv3040, were expressed and used to determine the immuno-reactivity of 100 serum samples. Antibody reactivity against rRv2031c, rRv3692, and rRv0444c was consistently observed. Among them, the best sensitivity and specificity of rRv3692 were 37% and 95% respectively. Furthermore, when rRv2031c and rRv3692 or rRv2031c, rRv3692, and rRv0444c were combined in 2:1 or equal amounts, the assay sensitivity and specificity were improved to 56.7% and 100% respectively.

Conclusions

These results suggest that Rv2031c, Rv3692, and Rv0444c are possible candidate biomarkers for effective use in the serodiagnosis of drug-resistant tuberculosis infections, and a combined formula of these antigens should be considered when designing a subunit assay kit.