Patent ID: 7888087

Claim:
A fusion protein comprising: (1) a first region selected from the group of: (a) a region having the amino acid sequence of SEQ ID NO: 1; (b) a region having variants of the amino acid sequence of SEQ ID NO: 1, wherein said variants have from one to eight deleted, substituted, inserted and/or added amino acids, and which has the ability to bind to the Fc region of IgG; and (c) a region which has an amino acid sequence that is at least approximately 94% identical to the amino acid sequence of SEQ ID NO: 1, and which has the ability to bind to the Fc region of IgG; and (2) a second region selected from the group of: (d) a region having the amino acid sequence of SEQ ID NO: 3; (e) a region having variants of the amino acid sequence of SEQ ID NO: 3, wherein said variants have from one to eight deleted, substituted, inserted and/or added amino acids, and which has the ability to bind to a peroxide of coelenterazine or a peroxide of a coelenterazine derivative so as to form a holoprotein that emits light under the action of a calcium ion; and (f) a region which has an amino acid sequence that is at least approximately 95% identical to the amino acid sequence of SEQ ID NO: 3, and which has the ability to bind to a peroxide of coelenterazine or a peroxide of a coelenterazine derivative so as to form a holoprotein that emits light under the action of a calcium ion, wherein the fusion protein has a minimum IgG-detection sensitivity of 1 ng/ml.