G proteins
The invention provides a mutant of a parent heterotrimeric G protein alpha (Gα) subunit, which mutant (i) lacks at least one helix of the helical domain of the parent Gα subunit; (ii) is capable of binding to a GPCR in the absence of a heterotrimeric G protein beta (Gβ) subunit and a heterotrimeric G protein gamma (Gγ) subunit; and (iii) has an amino acid sequence that contains one or more mutations compared to the amino acid sequence of the parent heterotrimeric Gα subunit, which mutations are selected from a deletion, a substitution and an insertion.
1. An engineered mutant of a naturally-occurring parent heterotrimeric G protein alpha (Gα) subunit, which mutant:
lacks the amino acid sequence of at least one of helix A (amino acids 85-113), helix B amino acids 123-136), helix C (amino acids 144-154), helix D (amino acids 157-168), helix E (amino acids 174-186), or helix F (amino acids 194-199) of the helical domain of the naturally-occurring parent Gα subunit, according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92;
is capable of binding to a GPCR in the absence of a heterotrimeric G protein beta (Gβ) subunit and a heterotrimeric G protein gamma (Gγ) subunit; and
has an amino acid sequence that contains one or more mutations compared to the amino acid sequence of the naturally-occurring parent heterotrimeric Gα subunit, which mutations are selected from a deletion, a substitution and an insertion;
wherein binding of the mutant Gα subunit to a GPCR increases the affinity of the GPCR for an agonist.
2. The mutant Gα subunit according to claim 1 , wherein the mutant lacks a region of the helical domain of the parent heterotrimeric Gα subunit corresponding to amino acid residues 70-193, 71-193, 85-193, or 85-199 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
3. The mutant Gα subunit according to claim 1 , wherein binding of the mutant Gα subunit to a GPCR activates the Gα subunit.
4. The mutant Gα subunit according to claim 3 , wherein activation of the Gα subunit generates a Gα protein signal in a cell.
5. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit has increased stability under denaturing conditions compared to its naturally-occurring parent Gα subunit or is expressed at a higher level than its parent Gα subunit, when expressed in a cell.
6. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit is able to stabilize a particular conformation of the GPCR upon binding to the GPCR.
7. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit is capable of binding to a nucleotide, such as a guanine nucleotide, or wherein the mutant Gα subunit is capable of binding to a Gβ and/or Gγ subunit of a heterotrimeric G protein.
8. The mutant Gα subunit according to claim 1 , wherein the Gα subunit is any one of a Gα s , Gα i/o , Gα q/11 , or Gα 12/13 subunit.
9. The mutant Gα subunit according to claim 1 , wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit is not deleted, wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit corresponds to amino acid residues 194-207 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
10. The mutant Gα subunit according to claim 1 , wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit is deleted, wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit corresponds to amino acid residues 194-207 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
11. The mutant Gα subunit according to claim 10 , wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit is replaced by a switch I region of a small GTPase, wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit corresponds to amino acid residues 194-207 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
12. The mutant Gα subunit according to claim 1 , wherein the helical domain or part thereof and/or the switch I region or part thereof, of the naturally-occurring parent heterotrimeric G protein alpha subunit is replaced by a linker sequence, wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit corresponds to amino acid residues 194-207 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
13. The mutant Gα subunit according to claim 1 , wherein the region of the parent heterotrimeric Gα subunit that corresponds to amino acid residues 65 to 203 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92, is deleted.
14. The mutant Gα subunit according to claim 13 , wherein the region of the naturally-occurring parent heterotrimeric Gα subunit is replaced by a linker sequence.
15. The mutant Gα subunit according to claim 1 , which, when compared to the naturally-occurring parent Gα subunit, has an N-terminally truncated amino acid sequence.
16. The mutant Gα subunit according to claim 1 which, when compared to the naturally-occurring parent Gα subunit, contains one or more mutations in the switch I region, wherein the switch I region of the naturally-occurring parent heterotrimeric G protein alpha subunit corresponds to amino acid residues 194-207 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
17. The mutant Gα subunit according to claim 1 , wherein the switch III region of the naturally-occurring parent heterotrimeric G protein alpha subunit is deleted, wherein the switch III region of the naturally-occurring parent heterotrimeric Gα subunit corresponds to amino acid residues 254-263 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
18. The mutant Gα subunit according to claim 1 , wherein the switch II region, or part thereof, of the naturally-occurring parent heterotrimeric Gα subunit, is replaced by a linker sequence, wherein the switch II region of the naturally-occurring parent heterotrimeric Gα subunit corresponds to amino acid residues 225-242 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
19. The mutant Gα subunit according to claim 1 , which, when compared to the naturally-occurring parent Gα subunit, has a different amino acid at a position which corresponds to any one or more of the following positions according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92: Val 36, His 41, Ala 48, Gly 49, Glu 50, Met 60, Leu 63, Leu 197, Cys 200, Arg 201, Phe 208, Asn 218, Gly 226, Glu 230, Ala 249, Ser 252, Leu 272, Ile 372, Val 375.
20. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit has at least 20% sequence identity to the amino acid sequence of the long isoform of human Gα-s subunit of SEQ ID NO:92.
21. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit has at least 20% sequence identity to any of the amino acid sequences of SEQ ID NOs: 1-45, 104-114, 116, 118, 120, or 122-139.
22. The mutant Gα subunit according to claim 1 , which, when compared to the naturally-occurring parent Gα subunit, comprises one or more dominant negative mutations.
23. The mutant Gα subunit according to claim 22 , which, when compared to the parent Gα subunit, has one or more different amino acids within the NKXD motif, wherein the NKXD motif of the naturally-occurring parent Gα subunit corresponds to amino acid residues 292-295 according to the numbering of the long isoform of human Gα-s subunit of SEQ ID NO:92.
24. The mutant Gα subunit according to claim 1 , wherein the mutant lacks helices A to E or lacks helices A to F of the helical domain of the parent Gα subunit.
25. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit has increased stability under denaturing conditions compared to its parent Gα subunit and is expressed at a higher level than its parent Gα subunit, when expressed in a cell.
26. The mutant Gα subunit according to claim 1 , wherein the mutant Gα subunit is capable of binding to a nucleotide, such as a guanine nucleotide, and wherein the mutant Gα subunit is capable of binding to a Gβ and/or Gγ subunit of a heterotrimeric G protein.