Shahar Dery

The development of native chemical ligation coupled with desulfurization has allowed ligation at several new ligation junctions. However, desulfurization also converts all cysteine residues in the protein sequence into alanine. Deselenization of selenocysteine, in contrast, selectively removes the selenol group to give alanine in the presence of unprotected cysteines. In this study we shed more light onto the deselenization mechanism of selenocysteine to alanine and provide optimized conditions for the reaction. The deselenization can be accomplished in one minute under anaerobic conditions to give alanine. Under aerobic conditions (oxygen saturation), selenocysteine is converted into serine.

Abstract N -heterocyclic carbenes (NHCs) have been widely utilized for the formation of self-assembled monolayers (SAMs) on various surfaces. The main methodologies for preparation of NHCs-based SAMs either requires inert atmosphere and strong base for deprotonation of imidazolium precursors or the use of specifically-synthesized precursors such as NHC(H)[HCO 3 ] salts or NHC–CO 2 adducts. Herein, we demonstrate an electrochemical approach for surface-anchoring of NHCs which overcomes the need for dry environment, addition of exogenous strong base or restricting synthetic steps. In the electrochemical deposition, water reduction reaction is used to generate high concentration of hydroxide ions in proximity to a metal electrode. Imidazolium cations were deprotonated by hydroxide ions, leading to carbenes formation that self-assembled on the electrode’s surface. SAMs of NO 2 -functionalized NHCs and dimethyl-benzimidazole were electrochemically deposited on Au films. SAMs of NHCs were also electrochemically deposited on Pt, Pd and Ag films, demonstrating the wide metal scope of this deposition technique.

Although native chemical ligation has enabled the synthesis of hundreds of proteins, not all proteins are accessible through typical ligation conditions. The challenging protein, 125-residue human phosphohistidine phosphatase 1 (PHPT1), has three cysteines near the C-terminus, which are not strategically placed for ligation. Herein, we report the first sequential native chemical ligation/deselenization reaction. PHPT1 was prepared from three unprotected peptide segments using two ligation reactions at cysteine and alanine junctions. Selenazolidine was utilized as a masked precursor for N-terminal selenocysteine in the middle segment, and, following ligation, deselenization provided the native alanine residue. This approach was used to synthesize both the wild-type PHPT1 and an analogue in which the active-site histidine was substituted with the unnatural and isosteric amino acid β-thienyl-l-alanine. The activity of both proteins was studied and compared, providing insights into the enzyme active site.

The human body contains 25 selenoproteins, which contain in their sequence the twenty-first encoded amino acid, selenocysteine. About a dozen of these proteins remain functionally uncharacterized or poorly studied. Challenges in accessing these selenoproteins using traditional recombinant expressions have prevented biological characterization thus far. Chemical protein synthesis has the potential to overcome these hurdles. Here we report the first total chemical syntheses of two human selenoproteins, selenoprotein M (SELM) and selenoprotein W (SELW). The synthesis of the more challenging protein SELM was enabled using recent advances in the field of selenocysteine chemistry. This approach allows the preparation of selenoproteins in milligram quantities and in homogenous form, which should open new horizons for future studies to pursue a fuller biological understanding of their role in health and disease.

Abstract The formation of flexible self‐assembled monolayers (SAMs) in which an external trigger modifies the geometry of surface‐anchored molecules is essential for the development of functional materials with tunable properties. In this work, it is demonstrated that NO 2 ‐functionalized N‐heterocyclic carbene molecules (NHCs), which were anchored on Au (111) surface, change their orientation from tilted into flat‐lying position following trigger‐induced reduction of their nitro groups. DFT calculations identified that the energetic driving force for reorientation was the lower steric hindrance and stronger interactions between the chemically reduced NHCs and the Au surface. The trigger‐induced changes in the NHCs′ anchoring geometry and chemical functionality modified the work function and the hydrophobicity of the NHC‐decorated Au surface, demonstrating the impact of a chemically tunable NHC‐based SAM on the properties of the metal surface.