New Phenol Esters for Efficient pH-Controlled Amine Acylation of Peptides, Proteins, and Sepharose Beads in Aqueous Media

Highly selective chemical modification of poly-His tagged peptides and proteins

Chemical modifications to proteins have wide applications. They may be used in, for example, the production of biopharmaceuticals and fluorescent probes. Despite their importance, highly regioselective chemical protein modifications are often challenging to achieve. We have developed two highly selective methods for protein acylation using poly-His tags inserted either at the N-terminus or in combination with a specific Lys residue. For this, we used an N-terminal Gly-His6 (Gly-His tag) or the sequence Hism-Lys-Hisn (Lys-His tag), respectively. The Gly-His tag directed the acylation to the N-terminal Nα-amine when reacted with 4-methoxyphenyl esters to yield stable conjugates. Next, the Lys-His tag was developed to allow modifications at the C-terminus or in loop regions of proteins. This gave a high selectivity of acylation of the designated Lys Nε-amine in the tag over native Lys residues in the protein under mild conditions. Here, we describe the synthesis of aromatic esters carrying different functionalities and reactivity tuning substituents on the phenol. The expression of poly-His tagged proteins, and the procedure for the highly selective peptide and protein acylations are detailed in this contribution. The versatility of these methods has been demonstrated by the attachment of different functionalities such as fluorophores, biotin, and azides to different proteins and an antibody.

Synthesis of peptide-siRNA conjugates via internal sulfonylphosphoramidate modifications and evaluation of their in vitro activity

Conjugates of therapeutic oligonucleotides (ONs) including peptide conjugates, provide a potential solution to the major challenge of specific tissue delivery faced by this class of drugs. Conjugations are often positioned terminal at the ONs, although internal placement of other chemical modifications are known to be of critical importance. The introduction of internal conjugation handles in chemically modified ONs require highly specialized and expensive nucleoside phosphoramidites. Here, we present a method for synthesizing a library of peptide-siRNA conjugates by conjugation at internal phosphorous positions via sulfonylphosphoramidate modifications incorporated into the sense strand. The sulfonylphosphoramidate modification offers benefits as it can be directly incorporated into chemically modified ONs by simply changing the oxidation step during synthesis, and furthermore holds the potential to create multifunctionalized therapeutic ONs. We have developed a workflow using a novel pH-controlled amine-to-amine linker that yields peptide-siRNA conjugates linked via amide bonds, and we have synthesized conjugates between GLP1 peptides and a HPRT1 siRNA as a model system. The in vitro activity of the conjugates was tested by GLP1R activity and knockdown of the HPRT1 gene. We found that conjugation near the 3'-end is more favorable than certain central internal positions and different internal conjugation strategies were compared.

From Natural Insulin to Designed Analogs: A Chemical Biology Exploration

Since its discovery in 1921, insulin has been at the forefront of scientific breakthroughs. From its amino acid sequencing to the revelation of its three-dimensional structure, the progress in insulin research has spurred significant therapeutic breakthroughs. In recent years, protein engineering has introduced innovative chemical and enzymatic methods for insulin modification, fostering the development of therapeutics with tailored pharmacological profiles. Alongside these advances, the quest for self-regulated, glucose-responsive insulin remains a holy grail in the field. In this article, we highlight the pivotal role of chemical biology in driving these innovations and discuss how it continues to shape the future trajectory of insulin research.

Enhancing activity of food protein-derived peptides: An overview of pretreatment, preparation, and modification methods

Food protein-derived peptides have garnered considerable attention due to their potential bioactivities and functional properties. However, the limited activity poses a challenge in effective utilization aspects. To overcome this hurdle, various methods have been explored to enhance the activity of these peptides. This comprehensive review offers an extensive overview of pretreatment, preparation methods, and modification strategies employed to augment the activity of food protein-derived peptides. Additionally, it encompasses a discussion on the current status and future prospects of bioactive peptide applications. The review also addresses the standardization of mass production processes and safety considerations for bioactive peptides while examining the future challenges and opportunities associated with these compounds. This comprehensive review serves as a valuable guide for researchers in the food industry, offering insights and recommendations to optimize the production process of bioactive peptides.

Development and Recent Advances in Lysine and N-Terminal Bioconjugation for Peptides and Proteins

The demand for creation of protein diversity and regulation of protein function through native protein modification and post-translational modification has ignited the development of selective chemical modification methods for peptides and proteins. Chemical bioconjugation offers selective functionalization providing bioconjugates with desired properties and functions for diverse applications in chemical biology, medicine, and biomaterials. The amino group existing at the lysine residue and N-terminus of peptides and proteins has been extensively studied in bioconjugation because of its good nucleophilicity and high surface exposure. Herein, we review the development of chemical methods for modification of the amino groups on lysine residue and N-terminus featuring excellent selectivity, mild reaction conditions, short reaction time, high conversion, biocompatibility, and preservation of protein integrity. This review is organized based on the chemoselectivity and site-selectivity of the chemical bioconjugation reagents to the amino acid residues aiming to provide guidance for the selection of appropriate bioconjugation methods.

Selective Acylation of Proteins at Gly and Lys in His Tags

The chemical modification of proteins is of great importance in chemical biology, biotechnology, and for the production of modified biopharmaceuticals, as it enables introduction of fluorophores, biotin, half-life extending moieties, and more. We have developed two methods that use poly-His sequences to direct the highly selective acylation of proteins, either at the N-terminus or at a specific Lys residue. For the former, we used an N-terminal Gly-His₆ segment (Gly-His tag) that directed acylation of the N-terminal N^α -amine with 4-methoxyphenyl esters, resulting in stable conjugates. Next, we developed the peptide sequences His_n -Lys-His_m (Lys-His tags) that direct the acylation of the designated Lys N^ϵ -amine under mild conditions and with high selectivity over native Lys residues. Both the Gly-His and Lys-His tags maintain the capacity for immobilized metal ion affinity chromatography. We have demonstrated the robustness of these methods by attaching different moieties such as azides, fluorophores, and biotin to different proteins, including antibodies.

Selective N-Terminal Acylation of Peptides and Proteins with Tunable Phenol Esters

Selective modification of peptides and proteins is of foremost importance for the development of biopharmaceuticals and exploring biochemical pathways, as well as other applications. Here, we present a study on the development of a general and easily applicable selective method for N-terminal acylation of biomolecules, applying a new type of phenol esters. Key to the success was the development of highly tunable phenol activators bearing in the ortho-position, sulfonic acid or sulfonamide, acting as a steric shield for hydrolysis, and electron-withdrawing groups in the other ortho- and para-position for controlling the reactivity of the activated phenol esters. A library of heptapeptides, testing all 20 natural amino acids positioned at the N-terminal, were acylated in a selective manner at the N-terminus. The majority showed high conversion and excellent N^α-selectivity. Several biologically relevant biomolecules, including DesB30 insulin and human growth hormone, could also be modified at the N-terminal in a highly selective way, exemplified by either a fluorophore or a fatty acid sidechain. Finally, taking advantage of the possibility to accurately adjust the reactivity of the phenol esters, we present a potential strategy for the construction of dual active biopharmaceuticals through the employment of a bifunctional acylation linker and demonstrate its use in the creation of a GLP-1 insulin analogue, coupled through the lysine residue of GLP-1 and the N-terminal Phe^B1 amine of DesB30 insulin.