N-terminal modifications

Rana, T.M., and Meares, C.F. (1990a) N-Terminal modification of immunoglobulin polypeptide chains tagged with isothiocyanato chelates. Bioconjugate Cbem. 1, 357-362. 

Kimuea, Y. et al. N-Terminal modifications of the 19S regulatory particle subunits of the yeast proteasome. Arch Biochcm Biophys 2003, 409, 341-8. 

Maytum, R., Geeves, M. A., and Konrad, M. (2000). Actomyosin regulatory properties of yeast tropomyosin are dependent upon N-terminal modification. Biochemistry 39, 11913-11920. 

Bacteriocins are antimicrobial peptides ribosomally synthesized in bacteria. These are classified into four or five classes.136 Class II bacteriocins are heat-stable nonlantibiotic peptides. Unlike lantibiotics described in the next section, class II bacteriocins are less modified disulfide bridge and some N-terminal modifications are known in some class II bacteriocins. It is well known that the biosynthesis of some of the class II bacteriocins is regulated by quorum sensing mediated by inducer peptide pheromones.95,137-1... 

Moser, B., Dewald, B., Barella, L., Schumacher, G., Baggiolini, M., and Glark-Lewis, I. (1993). Interleukin-8 antagonists generated by N-terminal modification. J. Biol. Chem. 268, 7125-7128. 

Dixon HBF. N-terminal modification of proteins—a review. J. Protein Chem. 1984 3 99-108. 

Wu P, Brand L. N-terminal modification of proteins for fluorescence measurements. Methods Enzymol. 1997 278 321-330. Gilmore JM, Scheck RA, Esser-Kahn AP, Joshi NS, Erancis MB. N-terminal protein modification through a biomimetic transamination reaction. Angew. Chem. Int. Ed. 2006 45 5307-5311. Christman KL, Broyer RM, Tolstyka ZP, Maynard HD. Site-specific protein immobilization through N-terminal oxime linkages. J. Mater. Chem. 2007 17 2021-2027. 

Although solution-based cyclization of linear peptides can be achieved with a slight excess of uronium salt without detectable N-terminal modification, on-resin cyclizations may be accompanied by significant guanidino formation. In such cases the use of phosphonium salts such as PyBOP or PyAOP (Section 3.7), which do not produce these side products, may be advantageous. 

Absolute identification of the modified amino acids may require more than one enzyme digest to produce different peptides. Some kinds of modifications that are easily identified by MS include phosphorylation of threonine or serine sulfation or phosphorylation of tyrosine deamidation of asparagine or glutamine O-or N-linked glycosylation oxidation of methionine or cysteine and N-terminal modification by formylation or prenylation. Combining enzymatic maps (tryptic mapping) with MS/MS may identify single amino acid variants of the protein that cannot otherwise be seen. 

N-terminal modifications methionine oc-amino N-methylmethionyl bacterial ribosomal and... 

The 8 h is to allow the polymerisation reaction to go to completion. In a crunch, this time may be shortened to as little as 1 h, but be aware that side-chain and N-terminal modification by acrylamide then becomes more of a problem. Gels may be allowed to polymerize as long as overnight provided that the butanol layer is increased so that it does not dry out. We also have stored gels at 4°C for up to 24 h. 

Acceptable accuracy and parallelism of the C-terminus assay are likely due to the C-terminal specificity of the capture antibody and the N-terminal location of the norleucine substitutions. Conversely, with the N-terminal specific assay, dramatic differences in recoveries were seen for the two forms of the drug, a direct consequence of these N-terminal modifications and differential binding of the immunoreagent directed at this region. Although each assay demonstrated good linearity upon... 

Both in the case of gastrin (53,97) and CCK (64,102) it was known that N-terminal modifications do not affect their bioactivity profile. Correspondingly, the N-terminus of gastrin and CCK was used for grafting the lipid moiety via the thiol/maleimide approach. For this purpose p-alanine was chosen as spacer of the maleimide group since the methylene moiety allows for sufficient flexibility without displacing too much the peptide chain from the double-tailed lipid. This fact was expected to allow more appropriate mimicry of natural lipids and thus, a better interdigitation with lipid bilayers. 

A critical consideration for N-terminal modification strategies is the ease with which the identity of the first amino acid can be established. Although all proteins begin with methionine as the first amino acid due to the commonality of the AUG start codon, this group is nearly always removed after translation in eukaryotes. The situation is more complicated in prokaryotes, however, as the methionyl aminopeptidases are sensitive to the size of the second amino... 

Fig. 10.3-13 A biomimetic strategy for transamination at pH 6.5 and at 22-37 °C. N-terminal modification. After condensation The resulting pyruvamides can be further with pyridoxal phosphate (PLP), a variety of derivatized through oxime formation. N-terminal amino acids undergo oxidative...

For a related reaction catalyzed by copper ions, see H.B.F. Dixon, N-terminal modification of... 

Spider venom peptides, toxic peptides from spiders that mainly modulate neurotransmission. Spider venoms are rich in neurotoxins that influence ion channels, interfere with neurotransmitter exocytosis, or affect neurotransmitter binding. The most important families are the atracotoxins (36-68 amino acids) and the latrotoxins. Many spider venom peptides are translated as prepropeptides and post-translationally modified, e.g., by disulfide bridge formation and C- or N-terminal modification. Because of the high diversity of its constituents, the spider venom is sometimes regarded as a biogenic structurally constrained combinatorial peptide library where nearly all amino acids of the mature sequence may be mutated, with the exception of a few strictly conserved cysteine residues responsible for the three-dimensional fold of the toxin [G. Estrada etal, Nat. Prod. Rep. 2007, 24,145]. 

Instead of using Cys-containing peptides it is convenient to use S-acetylmercaptoacetyl (SAMA) peptides for conjugation purposes. Unlike Cys, SAMA is not sensitive towards (air) oxidation during purification of the peptide. SAMA can be introduced into deprotected peptides in solution by reaction with N-succinimidyl S-acetylmercaptoacetate (18, 24). Selective introduction of SAMA can be achieved at the end of solid phase synthesis by N-terminal modification (Chapter 6) of the side-chain protected and resin-bound peptide with pentafluorophenyl 5-acetylmercaptoacetate (SAMA-OPfp) and 1-hydroxybenzotriazoIe (25). The thiol group of SAMA-peptides can be liberated by reaction with hydroxylamine. This S-deacetylation can be performed in the conjugation reaction mixture (25,26), i.e. in the presence of the sulphydryl-reactive protein Protocol 2). 

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