Screening

1. A method of selecting a binding partner of a GPCR, the method comprising:

a) providing a mutant GPCR of a parent GPCR, wherein the mutant GPCR has increased stability in a particular conformation under denaturing conditions relative to the parent GPCR in the same particular conformation under denaturing conditions;

b) providing one or more test compounds;

c) determining whether the or each test compound binds to the mutant GPCR when residing in a particular conformation; and

d) isolating one or more test compounds that bind to the mutant GPCR when residing in the particular conformation.

2. A method according to claim 1 , the method further comprising:

e) determining whether the or each test compound binds to the parent GPCR when residing in the particular conformation and

f) isolating the or each test compound that also binds the parent GPCR when residing in the particular conformation.

3. A method according to claim 1 , wherein the mutant GPCR is immobilised onto a solid support.

4. A method according to claim 1 , wherein more than one mutant GPCR is provided in step (a), it is determined whether the test compound binds to each mutant GPCR when residing in a particular conformation; and the test compound which binds to each mutant GPCR when residing in the particular conformation is isolated.

5. A method according to claim 1 , wherein more than one mutant GPCR is provided in step (a) and a test compound is selected that binds to a first mutant GPCR but which does not bind, or binds less strongly than to the first mutant GPCR, to at least one other mutant GPCR.

6. A method according to claim 1 , further comprising determining if the isolated test compound affects the function of the GPCR to which it binds.

7. A method according to claim 6 , wherein it is determined if the isolated test compound affects the binding of the GPCR to its natural ligand or analog thereof.

8. A method according to claim 7 , wherein the isolated test compound increases or decreases binding between the GPCR and its natural ligand or analog thereof.

9. A method according to claim 6 , wherein it is determined if the isolated test compound modulates activation of the GPCR to which it binds.

10. A method according to claim 9 , wherein the isolated test compound modulates any of calcium mobilisation, cAMP levels, kinase pathway activity, gene transcription from a reporter gene under control of the GPCR to which the test compound binds, β-arrestin recruitment, activation of G proteins, GTPase activity or [35S]GTPγS binding.

11. A method according to claim 9 , wherein the isolated test compound is an agonist test compound that increases activation of the GPCR to which it binds.

12. A method according to claim 9 , wherein the isolated test compound is an antagonist test compound that decreases activation of the GPCR to which it binds.

13. A method according to claim 1 , wherein the mutant GPCR is provided by:

(a) providing one or more mutants of a parent GPCR,

(b) selecting a ligand, the ligand being one which binds to the parent GPCR when the GPCR is residing in a particular conformation,

(c) determining whether the or each mutant GPCR has increased stability with respect to binding the selected ligand under denaturing conditions compared to the stability of the parent GPCR with respect to binding that ligand under denaturing conditions, and

(d) selecting those mutants that have an increased stability compared to the parent GPCR with respect to binding the selected ligand under denaturing conditions.

14. A method according to claim 1 , wherein the mutant GPCR is provided by:

(a) providing one or more mutants of a parent GPCR,

(b) selecting a ligand, the ligand being one which binds to the parent GPCR when the GPCR is residing in a particular conformation,

(c) determining whether the or each mutant GPCR has increased stability with respect to binding the selected ligand under denaturing conditions compared to the stability of the parent GPCR with respect to binding that ligand under denaturing conditions,

(d) selecting those mutants that have an increased stability compared to the parent GPCR with respect to binding the selected ligand,

(e) identifying the position or positions of the mutated amino acid residue or residues in the mutant GPCR or GPCRs which has been selected for increased stability, and

(f) synthesising a mutant GPCR which contains a replacement amino acid at one or more of the positions identified.

15. A method according to claim 1 , wherein the mutant GPCR is provided by:

(i) identifying in the amino acid sequence of one or more mutants of a first parent GPCR with increased stability in a particular conformation under denaturing conditions relative to the first parent GPCR in the same particular conformation under denaturing conditions, the position or positions at which the one or more mutants have at least one different amino acid residue compared to the first parent GPCR, and

(ii) making one or more mutations in the amino acid sequence that defines a second GPCR at the corresponding position or positions, to provide one or more mutants of a second parent GPCR with increased stability in a particular conformation under denaturing conditions relative to the second parent GPCR in the same particular conformation under denaturing conditions.

16. A method according to claim 1 , wherein the mutant GPCR is provided by:

(i) providing one or more mutants of a first parent GPCR with increased stability in a particular conformation under denaturing conditions relative to the first parent GPCR in the same particular conformation under denaturing conditions

(ii) identifying in a structural membrane protein model the structural motif or motifs in which the one or more mutants have at least one different amino acid residue compared to the first parent GPCR, and

(iii) making one or more mutations in the amino acid sequence that defines a corresponding structural motif or motifs in a second parent GPCR, to provide one or more mutants of a second parent GPCR with increased stability in a particular conformation under denaturing conditions relative to the second parent GPCR in the same particular conformation under denaturing conditions.

17. A method according to claim 15 , further comprising:

(I) selecting a ligand, the ligand being one which binds to the second parent GPCR when the GPCR is residing in a particular conformation

(II) determining whether the or each mutant of the second parent GPCR when residing in a particular conformation has increased stability with respect to binding the selected ligand compared to the stability of the second parent GPCR when residing in the same particular conformation with respect to binding that ligand, and

(III) selecting those mutants that have an increased stability compared to the second parent GPCR with respect to binding the selected ligand.