No abstract

Recently new lysine modifications were detected in histones and other proteins. Using the pyrrolysine amber suppression system we genetically inserted three of the new amino acids e-N-propionyl-, e-N-butyryl-, and e-N-crotonyl-lysine site specifically into histone H3. The lysine at position 9 (H3 K9), which is known to be highly modified in chromatin, was replaced by these unnatural amino acids.The histone code is based on the post-translational modification of critical amino acid residues in different histones. Among these, lysine acetylations and methylations are the most abundant and affect the transcriptional status of the genes associated with the corresponding histones. [1][2][3] The role of these modifications is sequence dependent. Typically acetylation is associated with transcriptionally active genes, while methylation induces transcriptional silencing. 4,5 Recently Zhao and co-workers discovered a number of new modified amino acids in histones. [6][7][8] Some of these were also detected in proteins other than histones, raising the possibility that they are of more widespread importance. [9][10][11] The new post-translational modifications (PTMs) are acylated derivatives of lysine at the e-amino position. The acylation partners are propionic acid, butyric acid, malonic acid, succinic acid, crotonic acid or fatty acids. A common characteristic of these compounds is that they are key metabolic intermediates that typically exist as CoA activated thioester species in the cell. 12 It is currently not clear how these newly discovered PTMs are biosynthetically established within the histones and we do not fully understand if and how they influence genetic processes.So far no specific deacylases for e-N-propionyl-or e-Nbutyryl-lysine have been identified. However Sirt5, a member of NAD-dependent sirtuins is able to specifically deacylate e-Nmalonyl-and e-N-succinyllysine. 11 Recently it was discovered that HDAC3 exhibits decrotonylase activity in vitro 13 and it was found that lysine crotonylation activates genes even in a globally repressive environment. 7,14 In order to enable investigation of the new lysine derivatives in histones it is essential to generate histones that contain these amino acids site specifically. 15 In this direction semi-synthetic chemical ligation based methods 16,17 were utilized and chemical methods were employed to generate acetyllysine (Kac) and methylated-lysines or derivatives thereof. [18][19][20][21] Chin and co-workers reported the introduction of Kac into H3 K56 22 using the pyrrolysine system. This system was also employed for the synthesis of monomethyl-and dimethyl-lysine containing histones. 23,24 Schultz et al. recently described the synthesis of histone H2B containing e-N-crotonyllysine at position K11 using an evolved pyrrolysyl-tRNA synthetase from Methanosarcina barkeri. 25 Here we show that the pyrrolysine system can be used to insert e-N-propionyl-(Kpr, 1), e-N-butyryl-(Kbu, 2), and e-Ncrotonyl-lysine (Kcr, 3) into histones at critical positions such as H3 K9 using...

Significant differences in the reactivity of norbornene derivatives in the inverse electron-demand Diels-Alder reaction with tetrazines were revealed by kinetic studies. Substantial rate enhancement for the exo norbornene isomers was observed. Quantum-chemical calculations were used to rationalize and support the observed experimental data.

Three for two: by using a Methanosarcina mazei PylRS triple mutant (Y306G, Y384F, I405R) the incorporation of two new exo-norbornene-containing pyrrolysine analogues was achieved. X-ray crystallographic analysis led to the identification of the crucial structural elements involved in substrate recognition by the evolved synthetase.

Effective and controlled drug delivery systems with on-demand release and targeting abilities have received enormous attention for biomedical applications. Here, we describe a novel enzyme-based cap system for mesoporous silica nanoparticles (MSNs) that is directly combined with a targeting ligand via bio-orthogonal click chemistry. The capping system is based on the pH-responsive binding of an aryl-sulfonamide-functionalized MSN and the enzyme carbonic anhydrase (CA). An unnatural amino acid (UAA) containing a norbornene moiety was genetically incorporated into CA. This UAA allowed for the site-specific bio-orthogonal attachment of even very sensitive targeting ligands such as folic acid and anandamide. This leads to specific receptor-mediated cell and stem cell uptake. We demonstrate the successful delivery and release of the chemotherapeutic agent Actinomycin D to KB cells. This novel nanocarrier concept provides a promising platform for the development of precisely controllable and highly modular theranostic systems.

To facilitate subcutaneous dosing, biotherapeutics need to exhibit properties that enable high-concentration formulation and long-term stability in the formulation buffer. For antibody–drug conjugates (ADCs), the introduction of drug-linkers can lead to increased hydrophobicity and higher levels of aggregation, which are both detrimental to the properties required for subcutaneous dosing. Herein we show how the physicochemical properties of ADCs could be controlled through the drug-linker chemistry in combination with prodrug chemistry of the payload, and how optimization of these combinations could afford ADCs with significantly improved solution stability. Key to achieving this optimization is the use of an accelerated stress test performed in a minimal formulation buffer.

We here report the construction of an E. coli expression system able to manufacture an unnatural amino acid by artificial biosynthesis. This can be orchestrated with incorporation into protein by amber stop codon suppression inside a living cell. In our case an alkyne-bearing pyrrolysine amino acid was biosynthesized and incorporated site-specifically allowing orthogonal double protein labeling.

We describe a new bioconjugation reaction based on the aziridination of norbornenes using electron-deficient sulfonyl azides. The reaction enables to attach various useful tags to peptides and proteins under mild conditions.Bioconjugation reactions substantially extend our ability to chemically manipulate proteins. Numerous chemical strategies for the attachment of synthetic molecules to proteins have been developed.1 Early approaches focused on native functional groups present on endogenous amino acids. 2 The main drawback of this approach is the lack of specificity since multiple copies of each amino acid are present in the primary protein structure. Unique recognition elements can be introduced into the protein structure to improve the selectivity of the ligation. One possibility is to add a specific amino acid sequence to the target protein that can be recognized by either an appropriate protein modifying enzyme 3 or by specific chemical probes. 4Another approach uses the biosynthetic machinery of the cell for incorporation of unnatural amino acids containing artificial functional groups. 5 We and others have used this approach for the incorporation of unnatural amino acids into proteins and have shown that the introduced functionality can be efficiently tagged by orthogonal chemical reactions. 6 The right choice of the reacting functional groups and the proper ligation technique plays a crucial role here. 7 Among other suitable functional groups that enable efficient protein labeling various derivatives of cyclooctyne, cyclooctene and cyclopropene have gained special attention in the field. 8 An extraordinary fast kinetic was observed especially in combination with tetrazines in inverse electrondemand Diels-Alder reactions or in dipolar cycloadditions with nitrile imines. 8a,b,e Unfortunately, the high reactivity of such systems is often accompanied by reduced stability and an increased tendency toward side reactions. 9 Moreover, synthetic access to these reagents often represents a considerable challenge. It is therefore desirable to develop a methodology that not only enables robust protein labeling but also utilizes easily available starting materials. Based on our experience using norbornenes as highly reactive compounds in combination with nitrile oxides, nitrile imines and tetrazines 10 we searched for reagents that do react with norbornenes, but also meet the criteria for better synthetic accessibility. Here we show that aziridination of norbornenes using electron-deficient sulfonyl azides represents an excellent balance between reactivity, stability and availability of the starting materials. We demonstrate that this reaction can be used for efficient labeling of norbornenecontaining peptides and proteins. Inspired by the pioneering studies on norbornene aziridination by Franz et al.,11 we decided to investigate whether this reaction can proceed in an aqueous environment and can be used for biomolecule labeling. Sulfonyl azides have been previously successfully applied as reagents for detectin...