Lysine modification

Figure 10. View of cytochrome c with positions of exposed heme edge (block) and lysine modifications (sequence numbers for a-carbons) shown. The smaller circles indicate the relative effectiveness of modifications on rate constants for the reaction of Cyt c(II) + PCu(II) ( see Table III). Preferential interaction with PCu(II) in the direction 25,27,13,87 is indicated.

Feeiman, R. N. and Tjian, R. Regulating the regulators lysine modifications make their mark. Cdl 2003, 112, 11-7. 

Detrimental effects of lysine modification (Maillard reactions) are not precluded. 

The extent of NA reduction at pH 4.2 was proportional to the extent of lysine modification when citraconic anhydride was used (see Figure 3). The NA was separated more effectively in the citraconylated yeast... 

Friedman, M. (1977). Effects of lysine modification on chemical, physical, nutritive, and functional properties of proteins. In "Food Proteins", J. R. Whitaker and S. R. Tannenbaum, Eds., Avi, Westport, Connecticut, pp. 446-483. 

The most common reagents for lysine modification are NHS-esters, which react with amines at rates that are significantly greater than background hydrolysis. Fig. 2a (13). These reagents are most commonly prepared from carboxylic acids and isolated before exposure to the protein substrate. Because of the popularity of this method, dozens of premade NHS-esters are now commercially available. In cases where aqueous solubility is problematic, sulfonated NHS-esters can be used. Because virtually all proteins have many lysine residues on their surface, this reaction affords the most reliable and general method... 

In a typical procedure (Kimmel 1967), an aqueous solution of a protein (10 mg/ml) is mixed at 4°C with an equal volume of O-methylisourea, adjusted to pH 9.5 with NaOH. The reaction is allowed to proceed for 4-5 days at 4°C, and is then terminated by dialysis against ice-cold deionized water. If lysine modification is found to be incomplete, the reaction may be attempted either at a higher temperature-(e.g. 25°C), or at pH 10.5-11 at 4°C. 

If amino acid analysis shows the lysine modification to be incomplete, the derivative is redissolved in the pH 9 buffer and the procedure repeated. Several such cycles may be necessary to achieve maximum modification of amino groups in native proteins. 

Reactive aldehydes derived from lipid peroxidation, which are able to bind to several amino acid residues, are also capable of generating novel amino acid oxidation products. By means of specific polyclonal or monoclonal antibodies, the occurrence of malonaldehyde (MDA) and 4-hydroxynonenal (4-HNE) bound to cellular protein has been shown. Lysine modification by lipid peroxidation products (linoleic hydroperoxide) can yield neo-antigenic determinants such as N-c-hexanoyl lysine. Both histidine and lysine are nucleophilic amino acids and therefore vulnerable to modification by lipid peroxidation-derived electrophiles, such as 2-alkenals, 4-hydroxy-2-alkenals, and ketoaldehydes, derived from lipid peroxidation. Histidine shows specific reactivity toward 2-alkenals and 4-hydroxy-2-alkenals, whereas lysine is an ubiquitous target of aldehydes, generating various types of adducts. Covalent binding of reactive aldehydes to histidine and lysine is associated with the appearance of carbonyl reactivity and antigenicity of proteins [125]. 

Zhao X et al (2005) Regulation of MEF2 by histone deacetylase 4- and SIRT1 deacetylase-mediated lysine modifications. Mol Cell Biol 25(19) 8456-8464... 

FIGURE 10. Proximity and ascorbic acid-mediated protein damage. The fragmentation of C-bovine serum albumin by 1 mM ascorbic acid over 3 hr with increasing concentrations of Cu (II) (0-50 puM) is shown. Lysine modification (up to 70%) of the protein was achieved by reductive methylation with formaldehyde. Methylated protein was unaffected by this derivatization (assessed by SDS-PAGE and analysis of histidine content) and appeared resistant to ascorbate-mediated fragmentation (Hunt, unpublished observation). 

The side chains of proteins can undergo post-translational modification in the course of thermal processes. The reaction can also result in the formation of protein cross-links. A known reaction which mainly proceeds in the absence of carbohydrates, for example, is the formation of dehydroalanine from serine, cysteine or serine phosphate by the elimination of H2O, H2S or phosphate. The dehydroalanine can then lead to protein cross-links with the nucleophilic side chains of lysine or cysteine (cf. 1.4.4.11). In the presence of carbohydrates or their degradation products, especially the side chains of lysine and arginine are subject to modification, which is accompanied by a reduction in the nutritional value of the proteins. The structures of important lysine modifications are summarized in Formula 4.95. The best known compounds are the Amadori product -fructoselysine and furosine, which can be formed from the former compound via the intermediate 4-deoxyosone (Formula 4.96). To detect of the extent of heat treatment, e. g., in the case of heat treated milk products, furosine is released by acid hydrolysis of the proteins and quantitatively determined by amino acid analysis. In this process, all the intermediates which lead to furosine are degraded and an unknown portion of already existing furosine is destroyed. Therefore, the hydrolysis must occur under standardized conditions or preferably by using enzymes. Examples showing the concentrations of furosine in food are presented in Table 4.13. 

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