Streptavidin iminobiotin binding

Raphael, M. R Rappole, C. A. Kurihara, L. K. Christodoulides, J. A. Qadri, S. N. Byers, J. M. Iminobiotin binding induces large fluorescent enhancements in avidin and streptavidin fluorescent conjugates and exhibits diverging pH-dependent binding affinities. J. Fluoresc. 2011,21,647-652. 

NHS-iminobiotin can be used to label amine-containing molecules with an iminobiotin tag, providing reversible-binding potential with avidin or streptavidin. The NHS ester reacts with proteins and other amine-containing molecules to create stable amide bond derivatives (Figure 11.6). An iminobiotinylated molecule then can be used to target and purify other... 

Figure 11.5 At pH 4, the protonated form of iminobiotin does not interact with the binding sites on avidin or streptavidin. At pH 11, the imino group is unprotonated and regains binding capability toward these proteins.

Another variable to consider in choosing biotinylation reagents is the use of a biotin analog such as iminobiotin that has a moderated affinity constant in its binding of avidin or streptavidin (Section 3.1). Analogs may be useful if release of the avidin—... 

The biotin-streptavidin system provides a "textbook case" of the relative free energies of the binding of biotin, aminobiotin, and thiobi-otin, as illustrated in Table 4.5. First, the calculated relative free energies are in reasonable agreement with experiment thiobiotin is calculated and observed to bind 10 or 4 kcal/ mol more weakly to streptavidin than biotin, and iminobiotin is calculated and observed to bind 10 or 7 kcdmol more weakly than biotin. What is more interesting are the energy components. Thiobiotin is easier to desolvate than biotin by kcal/mol (AG ni J but... 

Streptavidin is a biotin binding protein from Streptomyces avidinii with an extraordinary of 10 M . This extreme affinity means that elution from immobilised biotin required 6 M guanidine hydrochloride at pH 1.5. By using 2-iminobiotin as a ligand rather than biotin the protein can be purified in a single chromatography step [48]. This illustrates that it may be worthwhile to consider an alternative ligand to what may at first appear to be the obvious natural choice. 

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