Antibody-binding proteins

By applying a solution with the appropriate pH and ionic strength, the interaction between Protein A or Protein G and the antibody can be reversed, enabling easy renewal of sensing surfaces [32, 33]. This has been demonstrated by Yakovleva et al. 

FIGURE 5.6 Schematic representation of the immunosensor based on a Protein A-GEB biocomposite as a transducer, (a) Immobilization of RIgG on the surface via interaction with Protein A, (b) competitive immunoassay using anti-RIgG and biotinylated anti-RIgG, (c) enzyme labeling using HRP-streptavidin and (d) electrochemical enzyme activity determination. (Reprinted from [31] with permission from Elsevier.) 

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Biosensors may be classified into two categories biocatalytic biosensors and bioaffinity biosensors. Biocatalytic sensors contain a biocatalyst such as an enzyme to recognize the analytic selectively. Bioaflinity biosensors, on the other hand, may involve antibody, binding protein or receptor protein, which form stable complexes with the corresponding ligand. An immunosensor in which antibody is used as the receptor may represent a bioaflinity biosensor. 

Some species of pathogenic bacteria, notably Streptococci and Staphylococci, have proteins on their surface which bind immunoglobulins (1). Protein A from Staph, aureus and protein G from species of Streptococci, which are widely used as immunological tools, are the most extensively studied of these antibody-binding proteins. 

Biosensors are traditionally divided into two main classes. One class includes biosensors that use a biological receptor, and the other uses a biocatalyst. Examples of bio-receptors include antibodies, binding proteins, and lectins. A critical evaluation of bio-receptor-based biosensors has recently been published (1). 

Radioreceptor assay is a well established technique being increasingly utilized in both research and clinical medicine (1)(2). Details of this technique have been described in many publications, and for our purposes it is sufficient to say that these assays involve a competitive binding reaction between two major components, the binding material (antibody, binding protein, or membrane receptors) and the substances to be measured (hormones, drugs, enzymes, etc.). 

Mass spectrometry has been further used to study the post-translational modifications of viral proteins as well as the viral-antibody binding, protein-protein interactions and viral protein dynamics. 

Streptavidin [16] proteases (pepsin, papain, staphylococcus aureus V8 protease) [17] antibodies and antibody-binding proteins such as Protein A, Protein G or Protein M [18] lectins such as concanavalin and jacaUn [19]. 

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