OmpG variants
The present disclosure provides variant OmpG polypeptides, compositions comprising the OmpG variant polypeptides, and methods for using the variant OmpG polypeptides as nanopores for determining the sequence of single stranded nucleic acids. The variant OmpG nanopores reduce the ionic current noise versus the parental OmpG polypeptide from which they are derived and thereby enable sequencing of polynucleotides with single nucleotide resolution. The reduced ionic current noise also provides for the use of these OmpG nanopore variants in other single molecule sensing applications, e.g., protein sequencing.
1. A circular permutation variant of a parental outer membrane protein G (OmpG) polypeptide, the variant comprising a rearranged parental OmpG polypeptide in which a portion of the C-terminal end of the parental OmpG polypeptide comprising a beta strand is moved to the N-terminal end of the OmpG polypeptide,
wherein the parental OmpG polypeptide from which the variant is derived comprises (i) an amino acid sequence having at least 95% sequence identity to the amino acid sequence set forth as SEQ ID NO: 2 and (ii) a deletion of at least one loop-6 amino acid and
wherein the circular permutation variant retains the ability to form a nanopore.
2. The circular permutation variant of claim 1 , wherein the parental OmpG polypeptide further comprises a substitution at position Y50 of SEQ ID NO: 2 and/or deletion of D215 of SEQ ID NO: 2.
3. The circular permutation variant of claim 2 , wherein the parental OmpG polypeptide comprises a deletion of one or more loop-6 amino acids 216-227 of SEQ ID NO: 2, a deletion of amino acid D215 of SEQ ID NO: 2, and an A229 amino acid residue of SEQ ID NO: 2.
4. The circular permutation variant of claim 3 , wherein the parental OmpG polypeptide further comprises a mutation of one or more of amino acids R211, E15, R68, Y50, E152, E174, E17, D215, K114, E174, F66, or E31 of SEQ ID NO: 2.
5. The circular permutation variant of claim 4 , wherein the mutation comprises one or more of a R211N, R68N, Y50K, Y50N, or E17K mutation of SEQ ID NO: 2.
6. The circular permutation variant of claim 5 , wherein the mutation of SEQ ID NO: 2 is a Y50K amino acid substitution.
7. The circular permutation variant of claim 2 , wherein the parental OmpG polypeptide further comprises a deletion of one or more loop-6 amino acids of aminos acids 216-227 of SEQ ID NO: 2, a Y50K or Y50N amino acid substitution of SEQ ID NO: 2, and an A229 amino acid residue of SEQ ID NO: 2.
8. The circular permutation variant of claim 7 , wherein the parental OmpG polypeptide further comprises a mutation of one or more of amino acids R211, E15, R68, E152, E174, E17, D215, K114, E174, F66, or E31 of SEQ ID NO: 2.
9. The circular permutation variant of claim 8 , wherein the mutation is a D215 deletion of SEQ ID NO: 2.
10. The circular permutation variant of claim 8 , wherein the mutation comprises one or more of a R211N or R68N mutations of SEQ ID NO: 2.
11. The circular permutation variant of claim 2 , wherein the circular permutation variant has at least 95% sequence identity with residues 2-271 of SEQ ID NO: 17.
12. The circular permutation variant of claim 2 , wherein the parental OmpG polypeptide comprises a deletion of each of amino acids 218-229 of SEQ ID NO: 2.
13. The circular permutation variant of claim 12 , wherein the parental OmpG polypeptide further comprises an A217 residue of SEQ ID NO: 2.
14. The circular permutation variant of claim 13 , wherein the parental OmpG polypeptide further comprises Y50 substitution of SEQ ID NO: 2.
15. The circular permutation variant of claim 14 , wherein the substitution is a Y50K substitution.
16. The circular permutation variant of claim 13 , wherein the parental OmpG polypeptide further comprises an R68 substitution of SEQ ID NO: 2.
17. The circular permutation variant of claim 16 , wherein the substitution is a R68N substitution.
18. The circular permutation variant of claim 13 , wherein the parental OmpG polypeptide further comprises an R211 substitution of SEQ ID NO: 2.
19. The circular permutation variant of claim 18 , wherein the substitution is a R211N substitution.
20. The circular permutation variant of claim 13 , wherein the parental OmpG polypeptide further comprises an E17 substitution of SEQ ID NO: 2.
21. The circular permutation variant of claim 20 , wherein the substitution is a E17K substitution.
22. The circular permutation variant of claim 13 , wherein the parental OmpG polypeptide comprises a D215 deletion of SEQ ID NO: 2.
23. The circular permutation variant of claim 20 , wherein the parental OmpG polypeptide further comprises a Y50 substitution of SEQ ID NO: 2.
24. The circular permutation variant of claim 21 , wherein the Y50 substitution of SEQ ID NO: 2 is a Y50K substitution.