The combination of native chemical ligation and desulfurization is considered a powerful strategy in protein synthesis. Homogeneous desulfurization conditions based on a radical induced reaction have been widely used in the syntheses of various challenging proteins and their analogues. However, the presence of aryl thiols in the reaction mixture as a ligation catalyst hampers one-pot ligation/ desulfurization, hence mandating additional purification/lyophilization steps prior to desulfurization. This significantly reduces the yield and prolongs the ligation process. Here we report that the use of preformed peptide-aryl thioester allows for efficient one-pot ligation and desulfurization. This approach was tested successfully for various model peptides including the synthesis of ubiquitin from two fragments. However, in the case of the synthesis of di-ubiquitin chains, where the ligation is mediated by d-mercaptolysine to form an isopeptide bond, excess aryl thiol was required for efficient ligation, necessitating purification prior to desulfurization. To overcome these obstacles, we found that functionalization of the aryl thiol with a hydrazide moiety enabled, after the ligation step, its capture by resin-aldehyde to permit direct desulfurization. Altogether, these approaches should facilitate protein synthesis with improved efficiency in yields and time.
Deubiquitinases (DUBs) counteract ubiquitination by removing or trimming ubiquitin chains to alter the signal. Their diverse role in biological processes and involvement in diseases have recently attracted great interest with regard to their mechanism and inhibition. It has been shown that some DUBs are regulated by reactive oxygen species (ROS) in which the catalytic Cys residue undergoes reversible oxidation, hence modulating DUBs activity under oxidative stress. Reported herein for the first time, the observation that small molecules, which are capable of generating ROS efficiently, inhibit DUBs by selective and nonreversible oxidation of the catalytic Cys residue. Interestingly, the small molecule beta-lapachone, which is currently in clinical trials for cancer, is among the potent inhibitors, thus suggesting possible new cellular targets for its therapeutic effects. Our study describes a novel mechanism of DUBs inhibition and opens new opportunities in exploiting them for cancer therapy.
Deubiquitinases (DUBs) counteract ubiquitination by removing or trimming ubiquitin chains to alter the signal. Their diverse role in biological processes and involvement in diseases have recently attracted great interest with regard to their mechanism and inhibition. It has been shown that some DUBs are regulated by reactive oxygen species (ROS) in which the catalytic Cys residue undergoes reversible oxidation, hence modulating DUBs activity under oxidative stress. Reported herein for the first time, the observation that small molecules, which are capable of generating ROS efficiently, inhibit DUBs by selective and nonreversible oxidation of the catalytic Cys residue. Interestingly, the small molecule beta‐lapachone, which is currently in clinical trials for cancer, is among the potent inhibitors, thus suggesting possible new cellular targets for its therapeutic effects. Our study describes a novel mechanism of DUBs inhibition and opens new opportunities in exploiting them for cancer therapy.
Studying and targeting deubiquitinases is of high importance due to their various roles in cellular processes and involvement in diseases such as cancer. The recent development of unique probes and reagents using chemical synthesis of proteins became very instrumental in supporting these efforts. Here, we present a protein synthetic approach that enables the rapid synthesis of differently modified labeled-ubiquitinated peptides to facilitate rapid optimization of deubiquitinase substrates.
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