Conjugation of peptides and proteins

Fig. 49 Use of cyanogen bromide for the conjugation of peptides and proteins to polysaccharides...

Morpurgo, M., Veronese, F.M., Conjugates of peptides and protein polyethylene glycols. Methods Mol Biol. 283, 45-70, 2004. 

Reactions between a diene and a dienophile yielding cyclohexene derivatives through carbon-carbon or carbon-heteroatom bond formation are referred to as Diels-Alder (DA) reactions. The concerted [4 + 2] cycloaddition was first described in 1928 by Diels and Alder, ° and can be adapted for the efficient conjugation of peptides and proteins to synthetic polymers. Despite being recognized as highly selective and additive-free, DA reactions require elevated temperatures to obtain the desired product. Furthermore, the reversibility of the reaction limits its application in materials science. ... 

Some reports even indicate that the conjugation of proteins or peptides with carbohydrates can increase dramatically their activity compared to that of the native state (Susaki et al., 1998). Carbohydrates also can provide a protective effect on modified peptides toward proteolytic digestion (Rudd et al., 1994) or mask recognition of a peptide by the immune system (Harding et al., 1993). The creation of neoglycoproteins thus can affect the activity of peptides and proteins, which are not normally glycosylated in vivo. 

Native chemical ligation also can be extended to the conjugation of peptides or proteins to other molecules or surfaces. For instance, Reulen et al. (2007) prepared liposomes that contained cysteine-PEG-phospholipid derivatives and then coupled thioester-modified peptides or proteins to form a protein-liposome conjugate. Using this procedure, approximately 100 molecules of a collagen binding protein could be coupled to the cysteine-containing liposomes. 

Bemkop-Schntirch, A. and Scerbe-Saiko, A. (1998). Synthesis and in vitro evaluation of chitosan/EDTA/protease inhibitor conjugates which might be useful in oral delivery of peptides and proteins. Pharmaceut. Res., 15, 263-369. 

Atassi, M. Z., and Manshouri, T. (1991) Synthesis of tolerogenic monomethoxypolyethylene glycol and polyvinyl alcohol conjugates of peptides. J. Protein Chem. 10, 623—627. 

Pearson, PG., Slatter, J.G., Rashed, M.S., Han, D.H., Baillie, T.A. (1991). Carbamoylation of peptides and proteins in vitro by S-(N-methylcarbamoyl)GSH and S-(N-methylcarbamoyl)cysteine, two electrophilic S-linked conjugates of methyl isocyanate. Chem. Res. Toxicol. 4 436-44. 

The vitamin B12 receptor which facilitates uptake of the vitamin-intrinsic factor vitamin-binding protein complex has been used to enhance oral delivery and gastrointestinal uptake of peptides and proteins as their vitamin B12 conjugates (37). Commercial efforts are under way to exploit this receptor as well as the fetal Pc receptor which facilitates intestinal uptake of antibodies from colostrum/milk (38) and the polymeric immunoglobulin receptor which facilitates the serosal to mucosal transport of IgA and IgM (39). 

By analogy to the terms co- and posttranslational modifications of peptides and proteins to define these transformations in the in vivo biosynthesis, chemical manipulations at least theoretically can be carried out in a co- or postsynthetic manner. While nature exploits the sequence- and even conformation-dependent regioselectivity of enzymes to expand the molecular and functional diversity of peptides and proteins beyond the genetic code,P l synthetic chemical reactions are insufficient for the required selectivity even with the most advanced conjugation techniques. Therefore, the tactics usually employed involves a cosynthetic approach, i.e. synthesis of polypeptide chains with annino acid derivatives or... 

---