Single molecule peptide sequencing
Identifying proteins and peptides, and more specifically large-scale sequencing of single peptides in a mixture of diverse peptides at the single molecule level is an unmet challenge in the field of protein sequencing. Herein are methods for identifying amino acids in peptides, including peptides with unnatural amino acids. In one embodiment, the N-terminal amino acid is labeled with a first label and an internal amino acid is labeled with a second label. In some embodiments, the labels are fluorescent labels. In other embodiments, the internal amino acid is Lysine. In other embodiments, amino acids in peptides are identified based on the fluorescent signature for each peptide at the single molecule level.
1. A method for analyzing a polypeptide, comprising:
(a) providing said polypeptide immobilized to a support, wherein said polypeptide comprises at least one labeled internal amino acid;
(b) detecting at least one signal or signal change from said polypeptide immobilized to said support to identify at least a portion of a sequence of said polypeptide; and
(c) subjecting said polypeptide to conditions sufficient to remove at least one amino acid from said polypeptide.
2. The method of claim 1 , wherein said at least one amino acid is removed from an N-terminus of said polypeptide.
3. The method of claim 1 , wherein, subsequent to (c), said at least one labeled internal amino acid becomes a labeled terminal amino acid.
4. The method of claim 1 , wherein said at least one labeled internal amino acid is from a plurality of labeled amino acids, and wherein said at least one signal or signal change comprises a collective signal from said plurality of labeled amino acids.
5. The method of claim 4 , wherein said plurality of labeled amino acids comprise amino acids with different labels.
6. The method of claim 5 , wherein said different labels generate signals with different signal patterns.
7. The method of claim 1 , wherein said at least one labeled internal amino acid comprises one or more members selected from the group consisting of lysine, glutamate, and aspartate.
8. The method of claim 1 , wherein said at least one labeled internal amino acid comprises an amino acid having a label covalently attached thereto, which label generates said at least one signal or signal change.
9. The method of claim 1 , wherein said at least one labeled internal amino acid comprises an amino acid having a dye coupled thereto, which dye generates said at least one signal or signal change.
10. The method of claim 1 , wherein said at least one signal or signal change is an optical signal.
11. The method of claim 1 , wherein said at least one signal or signal change comprises a plurality of signals of different intensities.
12. The method of claim 1 , wherein said at least one signal or signal change comprises a plurality of signals of different frequencies or frequency ranges.
13. The method of claim 1 , wherein said at least one amino acid is removed from said polypeptide by a degradation reaction.
14. The method of claim 13 , wherein said degradation reaction is Edman degradation.
15. The method of claim 1 , wherein said polypeptide is a protein.
16. The method of claim 1 , wherein said polypeptide is part of a protein.
17. The method of claim 1 , wherein said at least one signal or signal change is detected with an optical detector having single-molecule sensitivity.
18. The method of claim 1 , further comprising processing said at least said portion of said sequence of said polypeptide against a reference sequence to identify said polypeptide or a protein from which said polypeptide is derived.
19. The method of claim 1 , further comprising, subsequent to (c), (i) identifying said at least said portion of said sequence of said polypeptide to identify said polypeptide, and (ii) using said polypeptide identified in (i) to quantify said polypeptide or a protein from which said polypeptide was derived.
20. The method of claim 1 , wherein in (a), less than all amino acids of said polypeptide are labeled.
21. The method of claim 1 , further comprising (i) repeating (b) and (c) to detect at least one additional signal or signal change from said polypeptide immobilized to said support and (ii) using (1) said at least one signal or signal change and (2) said at least one additional signal or signal change to identify said at least said portion of said sequence of said polypeptide.