Lysine groups

Figure 1.22 The solvent accessibility of lysine residues in the Fc region of an antibody is illustrated by highlighting the lysine groups in solid gray. Some lysine e-amine groups are extremely accessible to conjugation, while others are only partially exposed, making them difficult to modify in bioconjugation reactions.

Biocytin is e-N-biotinyl-L-lysine, a derivative of D-biotin containing a lysine group coupled at its e-amino side chain to the valeric acid carboxylate. It is a naturally occurring complex of biotin that is typically found in serum and urine, and probably represents breakdown products of recycling biotinylated proteins. The enzyme biotinidase specifically cleaves the lysine residue and releases the biotin component from biocytin (Ebrahim and Dakshinamurti, 1986, 1987). 

A similar transimination, in the reverse sense, takes place at the end of the reaction sequence to displace the product, but still retains PLP bound to the enzyme via the lysine group. Should the chemistry seem a little complicated, remind yourself... 

The resulting epitope density may depend on the number of lysine groups in the particular protein, and this will in turn affect the immunogenicity of the antigen. Trifluoroacyl adducts have been detected on the outer surface of hepatocytes, presumably as a result of the hapten-complex processing and delivery by MHC I, which is described above. The fact that the production of the trifluoroacetyl chloride is part of the major metabolic pathway and that the majority of patients produce trifluoroacylated proteins suggests that it is differences in the immune surveillance system or immune responsiveness, which determine which patients will succumb to the immunotoxic effect. 

The involvement of the lysine residues has been explored. Thus, trifluoroacetylation of lysine residues 13, 55 and 99 has been carried out,662 but only modification of residue 13 affects the reaction with cytochrome oxidase. Modification of lysine residues 13, 25, 27, 72 and 79 decreased the reaction rate of cytochrome c with cytochrome bs. It is possible that the lysine groups in unmodified cytochrome c interact with the carboxylate groups in cytochrome b5 (Asp-48, Glu-43, Glu-44 and Asp-60) and one of the heme propionate groups.663 In general, such studies support the proposal that these lysine groups represent binding sites for redox partners of cytochrome c. 

The importance of lysine groups around the heme-binding crevice in cytochrome c as binding groups for its redox partners has already been stressed, and has been demonstrated by chemical modification experiments.662 The question of whether there are different sites for binding of complex III and complex IV is not fully resolved. However, the same lysine residues are shielded from acetylation by complexing cytochrome c with either of these complexes,725 implying that they bind at the same site and that therefore entry and exit of the electron follows the same route. 

Agglutination of RBCs by polycations (e.g. polylysines) involves electrostatic attraction between the positively charged lysine groups of the polylysine molecule and the negatively charged N-acetylneuraminic acid on the RBC surface. Reduction of RBC surface charge by neuraminidase treatment markedly decreases the effectiveness of RBC agglutination by polylysine. 

As a consequence, interferon modified at the level of His34 with 12-kDa PEG maintains higher biological activity as compared to its counterpart prepared by 40-kDa PEG modification at the lysine groups, but has a much shorter duration of action. Tmax was ca. 20 h, the clearance was ten-fold higher than for interferon-PEG 40 kDa, and the volume of distribution was ca. 70 L, which is similar to that... 

A mathematical model of the putative binding of retinal to a lysine group at location 296 in opsin also appeared in 198996. Such a location would suggest a formulation such as 296, (N-retiny 1-ly sinejopsin. No laboratory confirmation of either model of a retinene attached to opsin through a Schiff-base has appeared. 

Organothiols chemisorbed on gold surfaces are especially usefiil for electrochemical and chemical studies. For example, carboxylic acid terminated monolayers are often used. An example is the attachment of cytochrome C with its side chain lysine groups to acid terminated self assembled monolayer gold electrodes. Carbodiimide mediated esterification of ferrocene-l,l -dicarboxylic acid with phenols is used to construct thermotropic liquid crystals. ... 

The count of side-chain amino groups corresponds to the analytical figure for lysine side chains in a denaturing solvent (8 Af urea). In the native protein, however, three of the thirteen lysine groups cannot be observed to titrate. The maximum positive proton charge ( S W" ") is however the same in the native and denatured states, within the uncertainty of about... 

Treatment of this enzyme with substrate and sodium boro-hydride leads to irreversible enzyme inactivation via in situ reduction of the enzyme-bound imine intermediate by boro-hydride, which indicates that a covalent link is formed. As mentioned, the pKa of this lysine group is abnormally low at 5.9, which is sufficiently low for it to act as a nucleophile at pH 7 (8). 

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