Method for producing a hetero-oligomeric pore comprising two different monomers in a specific stiochiometric ratio
The invention relates to a novel method of producing hetero-oligomeric pores. The invention also relates to hetero-oligomeric pores produced using the method and polynucleotide characterisation using the hetero-oligomeric pores.
1. A method for producing a hetero-oligomeric pore comprising two different monomers in a specific stoichiometric ratio, comprising:
(a) transfecting or transforming a cell with the first different monomer in a first vector, wherein expression of the first monomer is under the control of a first inducible promoter;
(b) transfecting or transforming the cell with the second different monomer in a second vector, wherein expression of the second monomer is under the control of a second inducible promoter that is not the same as the first inducible promoter; and
(c) controlling the concentration of a first inducing molecule relative to a second inducing molecule in the cell such that the first and second inducible promoters are simultaneously induced to produce the hetero-oligomeric pore comprising the first and second different monomers in the specific stoichiometric ratio,
wherein the specific stoichiometric ratio is not 1:1.
2. The method according to claim 1 , wherein the specific stoichiometric ratio of the first different monomer to the second different monomer is at least 5:1.
3. The method according to claim 1 , wherein at least one of the first and second different monomers is modified (i) to affect its expression compared with its expression in the absence of the modification and/or (ii) to affect its ability to oligomerise with itself or the other different monomer.
4. The method according to claim 1 , wherein the first inducible promoter and/or the second inducible promoter is an arabinose promoter, a propionate promoter, a rhamnose-inducible promoter, a xylose promoter or a lactose promoter.
5. A method for producing a hetero-oligomeric pore comprising two different monomers in a specific stoichiometric ratio, comprising:
(a) transfecting or transforming a cell with the first different monomer in a first vector, wherein expression of the first monomer is under the control of a first inducible promoter;
(b) transfecting or transforming the cell with the second different monomer in a second vector, wherein expression of the second monomer is under the control of a second inducible promoter that is not the same as the first inducible promoter, wherein the second different monomer is genetically fused to a peptide or polypeptide tag which reduces its ability to oligomerise with itself or reduces its expression compared with its expression in the absence of the tag; and
(c) simultaneously inducing the first and second inducible promoters such that the cell produces the hetero-oligomeric pore comprising the first and second different monomers in the specific stoichiometric ratio,
wherein the specific stoichiometric ratio is not 1:1.
6. The method according to claim 5 , wherein the peptide or polypeptide tag comprises:
(i) 4, 6, 8 or 10 consecutive arginine (R) residues or aspartic acid (D) residues; and/or (ii) 6 or 9 consecutive histidine (H) residues.
7. The method according to claim 1 , wherein the first different monomer and/or the second different monomer is genetically fused to a peptide or polypeptide tag, and wherein the method further comprises (d) purifying the hetero-oligomeric pore comprising the two different monomers in the specific stoichiometric ratio using the peptide or polypeptide tag.
8. The method according to claim 5 , wherein the second different monomer is genetically fused to the BasTL sequence (SEQ ID NO: 26) or a fragment thereof and wherein the BasTL sequence or fragment thereof is genetically fused at the carboxy (C) terminus of the second different monomer or wherein the BasTL sequence or fragment thereof is genetically fused at the carboxy (C) terminus of the second different monomer and separates the tag, if present, from the second different monomer.
9. The method according to claim 1 , wherein the first vector comprises a first selection marker and the second vector comprises a second selection marker.
10. The method according to claim 1 , wherein the cell is Escherichia coli.
11. The method according to claim 5 , wherein the peptide or polypeptide tag comprises serine-glycine (SG), asparagine-glycine-aspartic acid-serine (NGDS) or glycine-aspartic acid-serine-glycine (GDSG).
12. The method according to claim 9 , wherein the first and second selection markers are different from one another.
13. The method according to claim 1 , wherein the first inducible promoter is a rhamnose-inducible promoter and the second inducible promoter is an Isopropyl β-D-thiogalactopyranoside (IPTG)-inducible promoter.
14. The method according to claim 6 , wherein the tag comprises (a) 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 consecutive arginine (R) residues or aspartic acid (D) residues and/or (b) 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 consecutive histidine (H) residues.
15. The method according to claim 2 , wherein the specific stoichiometric ratio of the first different monomer to the second different monomer is 1:2, 2:1, 1:3, 3:1, 1:4, 2:3, 3:2, 4:1, 1:5, 1:6, 2:5, 3:4, 4:3, 5:2, 1:7, 3:5, 5:3, 1:8, 2:7, 4:5, 5:4, 7:2, 1:9, 3:7, 7:3, 5:1, 6:1, 7:1, 8:1 or 9:1.
16. The method according to claim 1 , wherein the first and/or second inducing molecule is a sugar molecule.
17. The method according to claim 13 , wherein the first inducing molecule is rhamnose and the second inducing molecule is IPTG.
18. The method according to claim 5 , wherein the specific stoichiometric ratio of the first different monomer to the second different monomer is 1:2, 2:1, 1:3, 3:1, 1:4, 2:3, 3:2, 4:1, 1:5, 1:6, 2:5, 3:4, 4:3, 5:2, 1:7, 3:5, 5:3, 1:8, 2:7, 4:5, 5:4, 7:2, 1:9, 3:7, 7:3, 5:1, 6:1, 7:1, 8:1 or 9:1.
19. The method according to claim 1 , wherein the pore is an MspA pore.
20. The method according to claim 5 , wherein the pore is an MspA pore.