Site-specific labeling of affinity tags in fusion proteins

A staining solution for detecting fusion proteins comprising a poly-histidine affinity tag, wherein said staining solution comprises:

• a) a fluorescent compound having formula A(L)m(B)n wherein A is a fluorophore, L is a linker, B is an acetic acid binding domain capable of selectively binding to a poly-histidine affinity tag, m is an integer from 1 to 4 and n is an integer from 1 to 6;
• and,
• b) a buffer having a pH of about 5 to 6.9 and comprising an acceptable counter ion with the proviso that said binding domain does not comprise an antibody or fragment thereof.

A method for selectively detecting an affinity tag containing fusion protein in a sample, said method comprising the steps of

• a) contacting said sample with a staining solution comprising a buffer and a fluorescent compound capable of selectively binding, directly or indirectly, to said affinity tag, wherein said fluorescent compound comprises a fluorophore;
• and,
• b) illuminating said fluorescent compound whereby said fusion protein is detected with the proviso that said fluorescent compound does not comprise an antibody or fragment thereof.

A kit for detecting an affinity tag containing fusion protein, wherein said kit comprises;

• a staining solution comprising a buffer and a fluorescent compound capable of selectively binding, directly or indirectly, to an affinity tag, wherein the fluorescent compound comprises a fluorophore;
• with the proviso that the fluorescent compound does not comprise an antibody or fragment thereof.

A fluorescent compound having formula A(L)m(B)n, wherein A is a fluorophore selected from the group consisting of borapolyazaindacene and coumarin, L is a linker, B is an acetic acid binding domain wherein said fluorescent compound contains at least three acetic acid groups that are capable of binding to a poly-histidine affinity tag, m is an integer from 1 to 4 and n is an integer from 1 to 6.

A composition comprising;

• a) a fluorescent compound capable of selectively binding, directly or indirectly, to affinity tag containing fusion protein, wherein said fluorescent compound comprises a fluorophore;
• and,
• b) a fusion protein comprising an affinity tag, provided said fluorescent compound does not comprise an antibody or fragment thereof.