Enzyme-pore constructs
The invention relates to constructs comprising a transmembrane protein pore subunit and a nucleic acid handling enzyme. The pore subunit is covalently attached to the enzyme such that both the subunit and enzyme retain their activity. The constructs can be used to generate transmembrane protein pores having a nucleic acid handling enzyme attached thereto. Such pores are particularly useful for sequencing nucleic acids. The enzyme handles the nucleic acid in such a way that the pore can detect its component nucleotides by stochastic sensing.
1. A method of attaching an enzyme to a transmembrane protein pore subunit comprising:
(a) providing a preparation of a first fusion protein, wherein each of the first fusion proteins comprise (i) an enzyme and (ii) a first polypeptide linker, wherein one end of the first polypeptide linker is attached to the carboxyl or amino terminus of the enzyme, and wherein the first polypeptide linker comprises an internal reactive lysine residue;
(b) providing a preparation of a second fusion protein, wherein each of the second fusion proteins comprise (i) a transmembrane protein pore subunit and (ii) a second polypeptide linker, wherein one end of the second polypeptide linker is attached to the carboxyl or amino terminus of the transmembrane protein pore subunit and wherein the second polypeptide linker comprises an internal reactive amino acid group having a carboxyl group that is specific for the reactive lysine in (a), and an affinity purification tag;
(c) performing a coupling reaction between the two fusion proteins of (a) and (b) above under suitable conditions such that the internal reactive lysine residue of the first linker covalently attaches to the internal reactive amino acid group of the second linker, thereby generating a population of enzyme-attached transmembrane protein pore subunits; and
(d) separating the preparation of enzyme-attached transmembrane protein pore subunits from any unreacted first fusion protein and second fusion protein.
2. A method according to claim 1 wherein the first polypeptide linker is attached to the carboxyl terminus of the enzyme.
3. A method according to claim 1 wherein the second polypeptide linker is attached to the carboxyl terminus of the transmembrane protein pore subunit.
4. A method according to claim 1 wherein the first polypeptide linker is attached to the carboxyl terminus of the enzyme and the second polypeptide linker is attached to the carboxyl terminus of the transmembrane protein pore subunit.
5. A method according to claim 1 wherein the enzyme is a nucleic acid handling enzyme.
6. A method according to claim 1 wherein the enzyme is a polymerase, exonuclease, helicase or topoisomerase.
7. A method according to claim 1 wherein the enzyme is capable of catalyzing the synthesis of a polymer.
8. A method according to claim 1 wherein the enzyme is a DNA polymerase or is an RNA polymerase.
9. A method according to claim 1 wherein the transmembrane protein pore subunit is from a β-barrel pore or an α-helix pore.
10. A method according to claim 1 wherein the transmembrane protein pore subunit is from α-hemolysin.
11. A method according to claim 5 , wherein the enzyme retains the ability to handle nucleic acids after being attached to the transmembrane protein pore subunit.
12. A method according to claim 7 , wherein the enzyme retains the ability to catalyze synthesis of a polymer after being attached to the transmembrane protein pore subunit.
13. A method according to claim 1 , wherein the transmembrane protein pore subunit retains its ability to form a pore after being attached to the enzyme.
14. The method of claim 1 further comprising, after step (d):
(e) combining the preparation of enzyme-attached transmembrane protein pore subunits with one or more wild-type transmembrane protein pore subunits to produce heteroligomeric transmembrane protein pores having a desired stoichiometry of enzyme-attached transmembrane protein pore subunits to wild-type subunits.
15. The method according to claim 14 , wherein the heteroligomeric transmembrane protein pores comprise an α-hemolysin transmembrane protein pore subunit.
16. The method according to claim 14 , wherein the enzyme attached to the heteroligomeric transmembrane protein pores is an exonuclease or a polymerase enzyme.
17. The method according to claim 14 , wherein the one or more wild-type transmembrane protein pore subunits are 5, 6, 7, or 8 wild-type transmembrane protein pore subunits.
18. The method of claim 14 , wherein the enzyme forms part of the cis side of the heteroligomeric transmembrane protein pores.
19. A method of attaching an enzyme to a transmembrane protein pore subunit comprising:
(a) providing a preparation of a first fusion protein, wherein each of the first fusion proteins comprise (i) transmembrane protein pore subunit and (ii) a first polypeptide linker, wherein one end of the first polypeptide linker is attached to the carboxyl or amino terminus of the transmembrane protein pore subunit, and wherein the first polypeptide linker comprises an internal reactive lysine residue;
(b) providing a preparation of a second fusion protein, wherein each of the second fusion proteins comprise (i) an enzyme and (ii) a second polypeptide linker, wherein one end of the second polypeptide linker is attached to the carboxyl or amino terminus of the enzyme and wherein the second polypeptide linker comprises an internal reactive amino acid group having a carboxyl group that is specific for the internal reactive lysine in (a), and an affinity purification tag;
(c) performing a coupling reaction between the two fusion proteins of (a) and (b) above under suitable conditions such that the internal reactive lysine residue of the first linker covalently attaches to the internal reactive amino acid group of the second linker, thereby generating a population of enzyme-attached transmembrane protein pore subunits; and
(d) separating the preparation of enzyme-attached transmembrane protein pore subunits from any unreacted first fusion protein and second fusion protein.
20. The method of claim 19 further comprising, after step (d):
(e) combining the preparation of enzyme-attached transmembrane protein pore subunits with one or more wild-type transmembrane protein pore subunits to produce heteroligomeric transmembrane protein pores having a desired stoichiometry of enzyme-attached transmembrane protein pore subunits to wild-type subunits.