Atop binding site

The structure of the ALR2 holoenzyme showed that the catalytic site was situated atop the nicotinamide moiety of the NADPH cofactor. The substrate binding site, which would determine the enzyme s specificity and also presumably bind inhibitors, appeared to be composed of a deep cleft (Figures 3 and 4). It extended away from the catalytic site towards the loop composed of residues between (34 and cc4 and the last 20 residues of the carboxy-terminal meander. This hypothesis was supported by the appearance of poorly resolved density that occupied this region, which suggested the presence of an endogenously bound substrate or inhibitor in the structure of the holoenzyme [16]. Subsequent studies indicate that this electron density may be a citrate molecule, one of the components included in the crystallization mixture. Activity studies indicate that citrate is indeed one of the many inhibitors of the enzyme with a K in the millimolar range [23]. 

The two-body part of the N—W potential was determined by fitting the full N—W potential (given the homogeneous part specified above) to the theoretically predicted values shown in Fig. 21. There is a strong dependence upon the binding site, at least between the atop vs. other sites. The lowest minimum is in very good agreement with the expierimental value of 6.73 eV... 

Figure 1 The two stable binding sites for a single Ni on graphite (a) hole site and (b) atop site. 

These intervention strategies can be considered as passive immunotherapy it may, however, be possible to actively immunize atopic individuals since there is evidence that neonatal or adult immunization with IgE can stimulate the formation of therapeutically useful anti-IgE auto-antibodies in animal systems (342). Their action suggests that the identification of structural determinants in IgE, which participate directly in IgE-receptor interaction, may form the basis for the development of peptide immunogens to induce the formation of antibodies, which can bind specifically to the receptor-binding sites of IgE in the circulation and to membrane IgE on B cells. Used as vaccines, such peptides could have a direct application in the treatment of all IgE-mediated allergies. 

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