Post base modifications

Farriol-Mathis, N., Garavelli, J.S., Boeckmann, B., Duvaud, S., Gasteiger, S.E., Gateau, E., Veuthey, A.-L., Bairoch, A. (2004). Annotation of post-translational modifications in the Swiss-Prot knowledge base. Proteomics 4, 1537. 

The formation of an aldehyde group on a macromolecule can produce an extremely useful derivative for subsequent modification or conjugation reactions. In their native state, proteins, peptides, nucleic acids, and oligonucleotides contain no naturally occurring aldehyde residues. There are no aldehydes on amino acid side chains, none introduced by post-translational modifications, and no formyl groups on any of the bases or sugars of DNA and RNA. To create reactive aldehydes at specific locations within these molecules opens the possibility of directing modification reactions toward discrete sites within the macromolecule. 

Plant-based production systems are now being used commercially for the synthesis of foreign proteins [1-3]. Post-translational modification in plant cells is similar to that carried out by animal cells plant cells are also able to fold multimeric proteins correctly. The sites of glycosylation on plant-produced mammalian proteins are the same as on the native protein however, processing of N-linked glycans in the secretory pathway of plant cells results in a more diverse array of glycoforms than is produced in animal expression systems [4]. Glycoprotein activity is retained in plant-derived mammalian proteins. 

Differences in post-translational modification (PTM) detail. Human therapeutic proteins produced in several recombinant systems (e.g. yeast-, plant- and insect-based systems Chapter 5) can display altered PTM detail, particularly in the context of glycosylation (Chapter 2). Some sugar residues/motifs characteristic of these systems can be highly immunogenic in humans. 

Although their ability to carry out post-translational modifications renders their use desira-ble/essential for producing many biopharmaceuticals, animal cell-based systems do suffer from a number of disadvantages. When compared with E. coli, animal cells display a very complex... 

Two important zeolite properties are (1) the intra-pore electrostatic field, and (2) its acid-base character. As discussed below post-synthetic modifications of many zeolites to fine-tune these properties are possible and provide a unique opportunity to influence reaction outcome. 

MS-Based Analysis of Post-Translational Modifications (PTMs)... 

Traditionally, prokaryotic expression, especially employment of E. coli-based vectors, has been the system of choice. However, bacteria are unable to provide many vital components required for post-translational modifications including various forms of glycosyla-tion or lipid attachment and protein processing, all of which can also be important for proper protein folding. For this reason, it is not surprising that much time and effort has been dedicated to the development of alternative systems, summarized in Tab. 1.2. 

The many (possibly more than 30) types of collagens found in human connective tissues have substantially the same chemical structure consisting mainly of glycine with smaller amounts of proline and some lysine and alanine. In addition, there are two unusual amino acids, hydroxyproline and hydroxylysine, neither of which has a corresponding base-triplet or codon within the genetic code. There is therefore, extensive post-translational modification of the protein by hydroxylation and also by glycosylation reactions. 

Strategies for functionalization have been developed that exploit the naturally occurring amino acids as well as the non-natural ones. Post-synthetic modifications have been reported that are based on reactive sites that self catalyze the incorporation of the new functionality at the side chains of Lys residues [24,25] and on the chemoselective ligation reaction [26-29]. These developments in combination with new methodology for the synthesis of large proteins [30] provide access to a highly versatile pool of new polypeptides and proteins. 

Stockwell, B.R., Haggarty, S.J. and Schreiber, S.L. (1999) High-throughput screening of small molecules in miniaturized mammalian cell-based assays involving post-translational modifications. Chemistry ei Biology,... 

Functional homopolymers can be synthesized by essentially two different methods. The first and more preferred way is to use a functional initiator which will ensure a high rate of chain end functionality. For instance, the polymerization of St initiated by a unimolecular terpyridine-functionalized nitroxide initiator yields well-defined PS homopolymers. The second technique is based on post-polymerization modifications. In this case, the reaction between mPEG and chloroterpyridine yields terpyridine-functionalized PEG building blocks, as illustrated in Scheme 13. 

The tRNAs undergo post-transcriptional modification to produce specialized bases, such as pseudouridine, dehydrouridine, and methylcytosine. 

The structures of some modified nucleosides found in tRNA. The parent ribonucleosides are shown on the left in yellow screens. The other bases found in RNA result from post-transcriptional modification. 

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