Polymer Conjugation

Following the initial positive results of conjugation of polymers to proteins based on simple conjugation methods, the chemistry has continued to experience advances with the development of new selective approaches of conjugation, some based on the exploitation of enzymes as tools to couple polymers and proteins or on genetic methods (e.g., thiol conjugation on an inserted cysteine or genetic code expansion with Amber codon technique). Among different techniques PEGylation has become the gold standard in this field. Protein PEGylation is primarily studied for prolonging the half-life of proteins by decreasing their body elimination, either through a reduced kidney clearance or a reduced liver clearance. Furthermore, PEGylation can also reduce the immunogenicity of non-human proteins by shielding the protein to the immune system.
In this field we investigated several polymers beside PEG, for example polyoxazolines, hyaluronic acid, polysialic acid, polyglutamic acids, etc.
To further extend the potentialities of polymer conjugation we thoroughly investigated the enzymatic conjugation approaches based on Transglutaminase. In nature, this enzyme catalyses the transfer of the acyl donor, the side chain of a methionine in a protein, to the amino donor, the side chain of a lysine in a second protein, thus forming a cross-link. The amino donor can be substituted by an amino group of a polymer for generating easily and rapidly homogenous conjugates in which the polymer is linked to single glutamines. We also demonstrated that transglutaminase can targeted the lysines of a protein when the acyl donor is the polymer, generating lysine coupled polymer-protein conjugates with the great advantage of selectivity of the transglutaminase.