Site-Specific Conjugation of Polymers to Proteins

Abstract

Conjugation of polymer to protein has been widely employed in therapeutics, medicine, biotechnology, and enzymatic catalysis. The synergistic effect benefits both counterparts and potentially overcomes their inherent limitations. This article reviews the strategies for the site-specific synthesis of well-defined protein-polymer conjugates, aiming to provide a toolbox for the community. First, it is essential to set a definite reactive site on the protein because the position of the reaction site can directly influence the reaction activity and the bioactivity of the protein after modification. The origins of the specific functional groups on protein include the utilization of the unique natural amino acid, mutagenesis to introduce a sole reactive amino acid, chemical modification, noncanonical amino acid incorporation, and enzyme-mediated introduction of functional groups. Second, the main conjugation methods, i.e., "grafting to" and "grafting from" methods, are summarized and compared with each other. In the "grafting to" method, a comprehensive investigation on the reactions used to attach an end functional polymer chain to a protein is conducted according to the position of the target site and its nature. In the "grafting from" method, a comparison between the commonly used controlled polymerization, i.e., atom transfer radical polymerization (ATRP) and reversible addition-fragmentation transfer (RAFT), is surveyed. Further, a special case where a noncovalent bond is adopted to link the protein and polymer together is investigated due to its high specificity and reversibility, typically biotin-(strept)avidin-based interactions and metal-mediated conjugation. Finally, applications of protein-polymer conjugates in drug delivery, biomedicine, biosensor, and the disease-related protein self-assembly are illustrated. This precise review on the conjugation of polymer chain to protein to form well-defined protein-polymer conjugates summarizes the representative strategies and may provide useful cues in the areas of biotechnology, therapeutic drugs, and biomedicine.

Transformation of Thioester‐Initiated Star Polymers into Linear Arms via Native Chemical Ligation

“…To be able to facilitate the undocking of the arms from the core, possible model reactions that involve modification of thioesters were explored. Carrying out such ligation chemistry could allow direct conjugation of a polymer to peptides over cysteine residues, which is otherwise known to be challenging …”

“…Carrying out such ligation chemistry could allow direct conjugation of a polymer to peptides over cysteine residues, which is otherwise known to be challenging. [24] In addition, cysteine could be used to force a transition of a thioester-initiated star polymer to a linear polymer. For this purpose, the star polymerization of (eDEGA) 200 was intentionally stopped in another experiment after 1 h to result in a well-defined polymer without any presence of side reactions (P8, M n,GPC = 9300 g mol −1 , PDI = 1.14, Figure S13, Supporting Information).…”

Tunable Polymeric Scaffolds for Enzyme Immobilization

“…In general terms, the main benefit of grafting to lies in that a broad spectrum of fully characterized preformed polymers can be attached to the enzymes, either site-specifically or randomly. However, there is a considerable issue with the attachment of bulky polymers or dendrimers that have intrinsic steric problems or hindered functional groups in their structure (Wang and Wu, 2018). Furthermore, a high grafting density is usually difficult to achieve using this approach (Carmali et al, 2017).…”

Pancreatic Ductal Adenocarcinoma: MicroRNAs Affecting Tumor Growth and Metastasis in Preclinical In Vivo Models

“…One of the issues is the improvement of the delivery systems. Optimization of liposomal carriers, conjugation of nucleic-acid related agents to poly-ethylene glycole (PEG), use of biodegradable polymers, cyclodextrin and dendrimers, have resulted in significant progress (127)(128)(129)(130)(131). Conjugation of miR-related agents to N-acetyl-D-galactosamine has significantly improved delivery to the liver based on its high affinity to the asialo glycoprotein receptor expressed in liver (132).…”