Total chemical synthesis of SUMO-2-Lys63-linked diubiquitin hybrid chains assisted by removable solubilizing tags

Total Chemical Synthesis of Modified Histones

In the post-genome era, epigenetics has received increasing attentions in recent years. The post-translational modifications (PTMs) of four core histones play central roles in epigenetic regulation of eukaryotic genome by either directly altering the biophysical properties of nucleosomes or by recruiting other effector proteins. In order to study the biological functions and structural mechanisms of these histone PTMs, an obligatory step is to prepare a sufficient amount of homogeneously modified histones. This task cannot be fully accomplished either by recombinant technology or enzymatic modification. In this context, synthetic chemists have developed novel protein synthetic tools and state-of-the-art chemical ligation strategies for the preparation of homologous modified histones. In this review, we summarize the recent advances in the preparation of modified histones, focusing on the total chemical synthesis strategies. The importance and potential of synthetic chemistry for the study of histone code will be also discussed.

Chemical synthesis of membrane proteins: a model study on the influenza virus B proton channel

NCL results in the quantitative yield of a membrane protein, where a thioester peptide is formed from an oxo-ester with an in situ cleavable solubilizing tag.

In the present study we have developed and optimized a robust strategy for the synthesis of highly hydrophobic peptides, especially membrane proteins, exemplarily using the influenza B M2 proton channel (BM2(1–51)). This strategy is based on the native chemical ligation of two fragments, where the thioester fragment is formed from an oxo-ester peptide, which is synthesized using Fmoc-SPPS, and features an in situ cleavable solubilizing tag (ADO, ADO₂ or ADO-Lys₅). The nearly quantitative production of the ligation product was followed by an optimized work up protocol, resulting in almost quantitative desulfurization and Acm-group cleavage. Circular dichroism analysis in a POPC lipid membrane revealed that the synthetic BM2(1–51) construct adopts a helical structure similar to that of the previously characterized BM2(1–33).

Chemical Synthesis of the Highly Hydrophobic Antiviral Membrane-Associated Protein IFITM3 and Modified Variants

Interferon-induced transmembrane protein 3 (IFITM3) is an antiviral transmembrane protein that is thought to serve as the primary factor for inhibiting the replication of a large number of viruses, including West Nile virus, Dengue virus, Ebola virus, and Zika virus. Production of this 14.5 kDa, 133-residue transmembrane protein, especially with essential posttranslational modifications, by recombinant expression is challenging. In this report, we document the chemical synthesis of IFTIM3 in multi-milligram quantities (>15 mg) and the preparation of phosphorylated and fluorescent variants. The synthesis was accomplished by using KAHA ligations, which operate under acidic aqueous/organic mixtures that excel at solubilizing even the exceptionally hydrophobic C-terminal region of IFITM3. The synthetic material is readily incorporated into model vesicles and forms the basis for using synthetic, homogenous IFITM3 and its derivatives for further studying its structure and biological mode of action.

Chemical Synthesis of the Highly Hydrophobic Antiviral Membrane-Associated Protein IFITM3 and Modified Variants

Interferon‐induced transmembrane protein 3 (IFITM3) is an antiviral transmembrane protein that is thought to serve as the primary factor for inhibiting the replication of a large number of viruses, including West Nile virus, Dengue virus, Ebola virus, and Zika virus. Production of this 14.5 kDa, 133‐residue transmembrane protein, especially with essential posttranslational modifications, by recombinant expression is challenging. In this report, we document the chemical synthesis of IFTIM3 in multi‐milligram quantities (>15 mg) and the preparation of phosphorylated and fluorescent variants. The synthesis was accomplished by using KAHA ligations, which operate under acidic aqueous/organic mixtures that excel at solubilizing even the exceptionally hydrophobic C‐terminal region of IFITM3. The synthetic material is readily incorporated into model vesicles and forms the basis for using synthetic, homogenous IFITM3 and its derivatives for further studying its structure and biological mode of action.

Sortase-mediated chemical protein synthesis reveals the bidentate binding of bisphosphorylated p62 with K63 diubiquitin

Phosphorylation of S403 or S407 of the autophagic receptor protein p62 has recently been discovered to enhance the binding of p62 with ubiquitinated protein substrates to upregulate selective autophagy. To elucidate the molecular mechanism of how phosphorylation regulates the recruitment of ubiquitinated proteins, we report the first chemical synthesis of homogeneously phosphorylated p62, which enables the setting up of accurate in vitro systems for biochemical studies. Our synthesis employs the technology of sortase A-mediated protein hydrazide ligation, which successfully affords three types of phosphorylated p62 at the multi-milligram scale. Quantitative biochemical measurements show that the binding affinity of S403/S407-bisphosphorylated p62 to K63 diubiquitin is significantly higher than that of mono-phosphorylated p62. This finding suggests that phosphorylated S403 and S407 sites should bind to different epitopes on the ubiquitin chain. Furthermore, glutamate mutation is found to give a significantly impaired binding affinity, implying the necessity of using chemically synthesized phosphorylated p62 for the biochemical study of selective autophagy.