Sites-specific modification

To date (ca 1996) many potentially usefiil sucrose derivatives have been synthesized. However, the economics and complexities of sucrochemical syntheses and the avadabiLity of cheaper substitutes have limited their acceptance hence, only a few of them are in commercial use. A change in the price and availability of petroleum feedstocks could reverse this trend. Additional impetus may come from regioselective, site-specific modifications of sucrose to produce derivatives to facilitate and improve the economics of sucrochemical syntheses. For example, the microbe yigwbacterium tumifaciens selectively oxidizes sucrose to a three-keto derivative, a precursor of alkylated sucroses for detergent use (50). Similarly, enzymes have been used for selective synthesis of specific sucrose derivatives (21). 

Fontana A, Spolaore B, Mero A, Veronese FM (2008) Site-specific modification and PEGylation of pharmaceutical proteins mediated by transglutaminase. Adv Dmg Deliv Rev... 

Bourel-Bonnet L, GrasMasse H, Melnyk O. A novel family of amphilic alpha-oxo aldehydes for the site-specific modification of peptides by two palmi-toyl groups in solution or in liposome suspensions. Tetrahedron Lett 2001 42 6851. 

Colman has also produced a definitive account of site-specific modification of enzymes, and her chapter is particularly instructive about the range and utility of reaction types that can be gainfully exploited in affinity labeling experiments. 

Wilson, M.E. and Whitesides, G.M. (1978) Conversion of a protein to a homogeneous asymmetric hydrogenation catalyst by site-specific modification with a dipho-sphinerhodium(l) moiety. J. Am. Chem. Soc., 100, 306-307. 

The assembly of complex RNA molecules, harboring site-specific modifications, is a multistep procedure that can be subdivided into three stages (Fig. 2.1) (i) preparation of unmodified RNA ligation precursor fragments, (ii) preparation of modified RNA ligation precursor fragments, and... 

Moore, M. J., and Sharp, P. A. (1992). Site-specific modification of pre-mRNA The 2,-hydroxyl groups at the splice sites. Science 256, 992—997. 

Fusion Cys-tag for Site-Specific Modification of Targeting Proteins... 

SCHEME 19.8 Site-specific modification of aldehydes. Ac, acetyl. 

Moore MJ, Sharp PA. Site-specific modification of pre-mRNA the... 

The site-specific modification of enzymes with a single electron-relay group located near to the redox cofactor and providing efficient electrical contact with the conductive support has been achieved by the reconstitution of enzymes with cofactors covalently linked to redox groups. Affinity interactions between enzymes and their cofactors at the electrode interface can allow the efficient electrical contacting of aligned proteins. 

D Agnillo, F. Alayash, A.I. Site-specific modifications and toxicity of blood substitutes, the case of diaspirin cross-linked hemoglobin. Adv. Drug Deliv. Rev. 2000, 40, 199-212. 

Because of the individual nature of the problems encountered, we have made no attempt to present detailed methodological information on site-specific modification. This is available in abundance in the books and reviews cited in ch. 1. 

Site-specific modification of native proteins with group-specific reagents... 

The site-specific modification of native proteins is not one of the routine procedures in protein chemistry. It cannot be placed in the same category as end-group labelling or determination of amino acid composition and sequence. The specific chemical modification of a native protein can never be guaranteed because the reactivity of amino acids in a native protein is rarely predictable even if the three-dimensional structure of the protein is known. Unusual pK s of side chains, steric and solvent effects and the proximity of the amino acid residue to a ligand-binding site all influence its reactivity, frequently in opposite directions. However certain well-defined avenues of in-... 

Many side-chain specific reagents have been successfully used for the stoichiometric modification of native proteins. This approach accounts for most of the papers published in this area. Although the likelihood of a successful site specific modification with these reagents is significantly less than that with a well designed affinity label, many more experiments with these compounds are probably attempted because minimal commitment of resources is necessary to initiate such studies. Most of the site-specific reagents are readily available, whereas affinity labels usually must be synthesized, often by difficult routes. 

The unexpected specificity which can be achieved with functional group modification reagents is an apparent consequence of the native protein s ability to impose a unique chemical environment on a given amino acid under a given set of experimental conditions. It is important to emphasize that the site-specific modification of a protein is a kinetic phenomenon and selective modifications result from the ability of the protein to alter the reaction rate of a single residue under one clearly defined condition of pH, ionic strength and temperature. For example, it is entirely possible that if, at pH 7.0, one lysine residue is substantially more reactive than either free lysine or other lysine residues in the protein it may well be less reactive than these at pH 9.0. 

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