Intein mediated peptide ligation

1. A method for preparing a target protein with a carboxy-terminal thioester, comprising:

(a) expressing a recombinant precursor protein in a host cell, the precursor protein comprising the target protein fused at its carboxy terminus to the amino terminus of an intein, the intein being selected from the group consisting of a native intein, an intein derivative, and a mutant intein, wherein the intein is optionally fused at its carboxy terminus to a binding protein domain; and,

(b) contacting the expressed precursor protein with 2-mercaptoethanesulfonic acid to induce cleavage of the intein from the precursor protein;

thereby forming the target protein having the carboxy-terminal thioester.

2. The method according to claim 1 , wherein the intein is selected from Saccharomyces cerevisiae Vma intein and Mycobacterium xenopi Gyr A intein.

3. The method according to claim 1 , wherein the binding protein domain is a chitin binding domain.

4. The method according to claim 1 , wherein the target protein is selected from a Bacillus stearothermophilus DNA polymerase I large fragment, thioredoxin or a cytotoxic protein.

5. The method according to claim 1 , wherein the binding protein domain is selected from a maltose binding protein and paramyosin.

6. A method for expressing a recombinant protein precursor, comprising:

(a) inserting a nucleic acid sequence encoding a target protein into a plasmid at a multiple cloning site located upstream of and in frame with a fusion gene encoding an intein and a binding protein domain, wherein

(i) the intein is selected from the group consisting of a native intein, an intein derivative, or a mutant intein; and

(ii) the multiple cloning site contains a linker having a nucleic acid sequence selected from the group consisting of SEQ ID NO:1; SEQ ID NO:2; SEQ ID NO:3; and SEQ ID NO:4; and

(b) transforming a host cell with the plasmid and providing conditions suitable for expressing the recombinant precursor protein by the host cell;

whereby the recombinant protein precursor is expressed.

7. The method of claim 6 , wherein the binding protein domain encoded by the fusion gene is a chitin binding protein.

8. The method according to claim 6 , wherein the plasmid is a pTXB plasmid.

9. A method of modifying a target protein by ligating a chemically synthesized peptide or protein to the target protein in vitro, comprising:

(a) expressing a recombinant precursor protein in a host cell, the precursor protein comprising the target protein fused at its carboxy terminus to the amino terminus of an intein selected from the group consisting of a native intein, an intein derivative, and a mutant intein, wherein the intein is optionally fused to a binding protein domain at its carboxy terminus;

(b) inducing cleavage of the intein from the target protein by contacting the precursor protein with 2-mercaptoethanesulfonic acid thereby forming a carboxy-terminal thioester on the target protein;

(c) obtaining the chemically synthesized peptide or protein having an amino terminal cysteine; and,

(d) ligating the target protein of step (b) to the chemically synthesized peptide or protein of step (c);

thereby forming a modified target protein.

10. The method according to claim 9 , wherein the protein after modification is a cytotoxic protein.

11. A method of labeling a target protein comprising:

(a) expressing a recombinant precursor protein in a host cell, the precursor protein comprising the target protein fused at its carboxy terminus to the amino terminus of an intein, the intein being selected from the group consisting of a native intein, an intein derivative, and a mutant intein, wherein the intein is optionally fused at its carboxy terminus to a binding protein domain;

(b) inducing cleavage of the intein from the target protein by contacting the precursor protein with 2-mercaptoethanesulfonic acid thereby forming a carboxy-terminal thioester on the target protein;

(c) obtaining a chemically synthesized peptide or protein having a marker and an amino-terminal cysteine; and,

(d) ligating the target protein of step (b) to the chemically synthesized peptide or protein of step (c);

thereby forming the labeled target protein.

12. The method according to claim 11 , wherein the marker is selected from the group consisting of a fluorescent marker, a spin label, an affinity tag, and a radiolabel.

13. The method according to claim 11 , wherein the chemically synthesized peptide or protein is an antigenic determinant.

14. A method of restoring a biological activity to a polypeptide inactive due to the absence of a carboxyl proximal amino acid sequence region by ligating a chemically synthesized protein or peptide comprising a carboxyl proximal amino acid sequence region of the polypeptide to the polypeptide lacking said region, comprising:

(a) expressing a recombinant fusion protein in a host cell, the fusion protein comprising the inactive form of the polypeptide fused at its carboxy terminus to the amino terminus of an intein, the intein being selected from the group consisting of a native intein, an intein derivative, and a mutant intein, wherein the fusion protein is expressed from a plasmid;

(b) inducing cleavage of the intein from the inactive form of the polypeptide by contacting the fusion protein of step (a) with 2-mercaptoethanesulfonic acid thereby forming a carboxy-terminal thioester on the inactive form of the polypeptide;

(c) obtaining a chemically synthesized peptide or protein having an amino-terminal cysteine; and,

(d) ligating the inactive form of the polypeptide having a carboxy-terminal thioester produced in step (b) to the chemically synthesized peptide or protein of step (c);

thereby restoring a biological activity of the polypeptide.

15. The method according to claim 14 , wherein the polypeptide to which ligation with a carboxyl proximal amino acid sequence region restores a biological activity is a cytotoxic protein.

16. The method of claim 15 , wherein the cytotoxic protein is a restriction endonuclease.