Method for sequencing a heteropolymeric target nucleic acid sequence
The invention relates to a method for sequencing a heteropolymeric target nucleic acid sequence that involves stochastic sensing. The invention also relates to a method for improving a pore for sequencing a target nucleic acid sequence by modifying one or more sites in the pore.
1. A method of preparing an apparatus for sequencing a target nucleic acid sequence, comprising:
(i) obtaining a nucleic acid sequence encoding an unmodified transmembrane protein pore monomer;
(ii) modifying the nucleic acid sequence, wherein the modified nucleic acid sequence encodes a modified transmembrane protein pore monomer that comprises one or more amino acid substitutions that alter the size, conformation, or net charge of the modified transmembrane protein pore monomer relative to the unmodified transmembrane protein pore monomer;
(iii) forming a modified transmembrane protein pore comprising at least six transmembrane protein pore monomers, wherein at least one of the transmembrane protein pore monomers is the modified transmembrane protein pore monomer encoded by the modified nucleic acid sequence of (ii), and the resulting modified transmembrane protein pore comprises a channel that has only two distinct sites capable of distinguishing between different nucleotides, and wherein the only two distinct sites of amino acids are separated from each other by between 10 and 50 angstroms; and
(iv) inserting the modified transmembrane protein pore into a membrane to form the apparatus.
2. The method according to claim 1 , wherein modifying the nucleic acid sequence comprises modifying the nucleic acid sequence to introduce in the modified transmembrane protein pore monomer: (i) substitution of one or more neutrally charged or negatively charged amino acids with positively charged amino acids and/or (ii) substitution of one or more neutrally charged or positively charged amino acids with negatively charged amino acids.
3. The method according to claim 1 , wherein the only two distinct sites of amino acids are each capable of discriminating between different nucleotides in a different manner.
4. The method according to claim 1 , wherein the modified transmembrane protein pore is a transmembrane protein pore derived from α-hemolysin (α-HL).
5. The method according to claim 4 , wherein the modified transmembrane protein pore comprises seven subunits that form a barrel.
6. The method according claim 1 , wherein the modified transmembrane protein pore does not contain a molecular adaptor.
7. The method according to claim 1 , wherein the membrane is a lipid bilayer.
8. The method of claim 1 , wherein the modified transmembrane protein pore is a homo-oligomeric pore.
9. The method of claim 1 , wherein the modified transmembrane protein pore is a hetero-oligomeric pore.
10. The method of claim 9 , further comprising purifying the modified transmembrane protein pore between steps (iii) and (iv).