| 摘要 |
Circularly permuted proteins are described wherein the natural termini of the polypeptide are joined and the resulting circular protein is opened at another point to create new C- and N- termini. The resulting protein exhibits some altered characteristic such as reduced substrate binding, for example. Fusion proteins can be made from the circularly permuted protein by attaching the second polypeptide to these newly created termini. These fusion proteins will have altered properties from a fusion protein made by attaching the second polypeptide to the natural termini. For example, the second peptide or protein can be attached at a position where it is more accessible to its substrate or intended target. In the preferred embodiment, the base circularly permuted biotin binding protein. In one embodiment, a flexible polypeptide loop important for the binding of biotin was opened by creation of the circularly permuted protein. The original termini (residues 13 and 139 of SEQ ID NO:1) were joined by a linker. The biotin association constant was reduced approximately six orders of magnitude below that of wild type streptavidin to 107 M-1. Fusion proteins of the circularly permuted streptavidin can be made with secondary peptides/proteins such as IgG binding protein A or single-chain antibodies.
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