Structural prerequisites for G-protein activation by the neurotensin receptor.

We previously determined the structure of neurotensin receptor NTSR1 in an active-like conformation with six thermostabilizing mutations bound to the peptide agonist neurotensin. This receptor was unable to activate G proteins, indicating that the mutations restricted NTSR1 to relate agonist binding to G-protein activation. Here we analyse the effect of three of those mutations (E166A(3.49), L310A(6.37), F358A(7.42)) and present two structures of NTSR1 able to catalyse nucleotide exchange at Gα. The presence of F358(7.42) causes the conserved W321(6.48) to adopt a side chain orientation parallel to the lipid bilayer sealing the collapsed Na(+) ion pocket and linking the agonist with residues in the lower receptor part implicated in GPCR activation. In the intracellular receptor half, the bulkier L310(6.37) side chain dictates the position of R167(3.50) of the highly conserved D/ERY motif. These residues, together with the presence of E166(3.49) provide determinants for G-protein activation by NTSR1.