Devices, systems, and methods for single molecule, real-time nucleic acid sequencing
Methods, systems, and reagents for real-time single molecule sequencing of nucleic acids, particularly long DNA molecules, is described. Preferably, such methods and systems combine FRET (Förster Resonance Energy Transfer)-based proximity sensing of labeled nucleotides in or near a DNA polymerase's active site with FRET-based monitoring of the conformational changes in the polymerase that occur during nucleotide incorporation.
1. A method of single-molecule, real-time nucleic acid sequencing-by-synthesis, comprising:
a. performing on a solid substrate a plurality of single-molecule, real-time nucleic acid molecule sequencing-by-synthesis reactions using a plurality of independently resolvable polymerase-template complexes,
wherein each independently resolvable polymerase-template complex comprises a polymerase enzyme and a nucleic acid template, which nucleic acid template comprises a priming region complementary to a primer that can be extended by addition of one or more nucleotides by the polymerase enzyme to form an extension product,
wherein the polymerase enzyme has been modified to allow (i) proximity sensing of at least one labeled nucleotide analogue species when a molecule of the labeled nucleotide analogue species associates with the polymerase enzyme proximate to the nucleic acid template; and (ii) sensing of a conformational change in the polymerase enzyme upon polymerase-mediated addition of a labeled nucleotide analogue to the primer or extension product,
wherein sensing the conformation change comprises a first FRET from a first energy donor moiety attached to the polymerase enzyme at a first position to an intermediate energy acceptor/donor moiety attached to the polymerase enzyme at a second position when a conformational change in the polymerase enzyme occurs upon polymerase-mediated addition of a nucleotide to the primer or extension product, and
wherein the proximity sensing comprises a second FRET from the intermediate energy acceptor/donor moiety to a second energy acceptor moiety of a labeled nucleotide analogue species when a molecule of the labeled nucleotide analogue species associates with the polymerase enzyme proximate to the nucleic acid template in a position associated with extension, which second FRET results in fluorescence indicative of the identity of the labeled nucleotide analogue species incorporated into the extension product;
b. exposing the solid substrate and polymerase-template complexes to a sequencing reaction mixture comprising primers and a plurality of nucleotide analogue species, each of which is a different labeled nucleotide analogue species, wherein each of the different labeled nucleotide analogue species comprises a second energy acceptor moiety having a fluorescence spectrum that resolvably differs from the fluorescence spectra of the other labeled nucleotide analogue species;
c. allowing sequencing reactions by the polymerase-template complexes, primers, and nucleotide analogue species to proceed;
d. detecting fluorescence events from the sequencing reactions; and
e. for a given independently resolvable polymerase-template complex, calling a nucleotide addition corresponding to the labeled nucleotide analogue species when, at substantially the same time, (i) proximate association of the labeled nucleotide analogue species and polymerase enzyme and (ii) and a conformational change in the polymerase enzyme, is sensed.
2. A method of single-molecule, real-time nucleic acid sequencing-by-synthesis, comprising:
a. performing on a solid substrate a plurality of single-molecule, real-time nucleic acid molecule sequencing-by-synthesis reactions using a plurality of independently resolvable polymerase-template complexes,
wherein each independently resolvable polymerase-template complex comprises a polymerase enzyme and a nucleic acid template, which nucleic acid template comprises a priming region complementary to a primer that can be extended by addition of one or more nucleotides by the polymerase enzyme to form an extension product,
wherein the polymerase enzyme has been modified to allow (i) proximity sensing of at least one labeled nucleotide analogue species when a molecule of the labeled nucleotide analogue species associates with the polymerase enzyme proximate to the nucleic acid template; and (ii) sensing of a conformational change in the polymerase enzyme upon polymerase-mediated addition of a labeled nucleotide analogue to the primer or extension product,
wherein sensing the conformational change comprises a first FRET from an energy donor moiety attached at a first position of the polymerase enzyme to a first energy acceptor moiety attached to the polymerase at a second position when a conformational change in the polymerase enzyme occurs upon polymerase-mediated addition of a labeled nucleotide analogue to the primer or extension product, which first FRET results in fluorescence indicative of the conformational change in the polymerase enzyme that occurs when a nucleotide analogue species is incorporated into the extension product, and
wherein the proximity sensing comprises a second FRET from the energy donor moiety to a second energy acceptor moiety of a labeled nucleotide analogue species when a molecule of the labeled nucleotide analogue species associates with the polymerase enzyme proximate to the nucleic acid template in a position associated with extension, which second FRET results in fluorescence indicative of the identity of the labeled nucleotide analogue species incorporated into the extension product;
b. exposing the solid substrate and polymerase-template complexes to a sequencing reaction mixture comprising primers and a plurality of nucleotide analogue species, each of which is a different labeled nucleotide analogue species, wherein each of the different labeled nucleotide analogue species comprises a second energy acceptor moiety having a fluorescence spectrum that resolvably differs from the fluorescence spectra of the other labeled nucleotide analogue species;
c. allowing sequencing reactions by the polymerase-template complexes, primers, and nucleotide analogue species to proceed;
d. detecting fluorescence events from the sequencing reactions; and
e. for a given independently resolvable polymerase-template complex, calling a nucleotide addition corresponding to the labeled nucleotide analogue species when, at substantially the same time, (i) proximate association of the labeled nucleotide analogue species and polymerase enzyme and (ii) and a conformational change in the polymerase enzyme, is sensed.
3. A method according to claim 1 , wherein the sequencing-by-synthesis reactions comprise four different nucleotide analogue species, some or all of which are differentially labeled such that each labeled nucleotide analogue species can be distinguished from the other labeled nucleotide analogue species.
4. A method according to claim 1 , wherein addition of nucleotide analogue residues to primers or extension products is detected using fluorescence or electronically.
5. A method according to claim 1 , wherein addition of nucleotide analogue residues to primers or extension products is detected by electrochemistry, capacitance, conductivity, impedance, or with a field effect transducer.
6. A method according to claim 1 , wherein addition of nucleotide analogue residues to primers or extension products is detected by Förster resonance energy transfer (FRET) or total internal reflectance fluorescence (TIRF) or using a zero-mode waveguide or a plasmonic antenna.
7. A method according to claim 1 , wherein (i) a 3′ region of the nucleic acid template is attached directly or indirectly to the solid substrate, or (ii) an oligonucleotide complementary to a sequence of nucleotides in the nucleic acid template is attached directly or indirectly to the solid substrate.
8. A method according to claim 7 , wherein at least one extension product binds to at least one proximate secondary DNA binding site on the substrate.
9. A method according to claim 8 , wherein binding of the extension product at the proximate secondary DNA binding site is mediated by a DNA anchoring agent attached to the substrate, wherein the DNA anchoring agent optionally is a dsDNA binding antibody or antigen binding fragment thereof, a DNA binding protein or DNA-binding fragment thereof, or a small molecule that binds dsDNA.
10. A method according to claim 1 , wherein the polymerase enzyme is attached to or immobilized on the substrate.