Conformational Changes in Tyrosine 11 of Neurotensin Are Required to Activate the Neurotensin Receptor 1.

Cell-cell communication via endogenous peptides and their receptors is vital for controlling all aspects of human physiology and most peptides signal through G protein-coupled receptors (GPCRs). Disordered peptides bind GPCRs through complex modes for which there are few representative crystal structures. The disordered peptide neurotensin (NT) is a neuromodulator of classical neurotransmitters such as dopamine and glutamate, through activation of neurotensin receptor 1 (NTS ₁ ). While several experimental structures show how NT binds NTS ₁ , details about the structural dynamics of NT during and after binding NTS ₁ , or the role of peptide dynamics on receptor activation, remain obscure. Here saturation transfer difference (STD) NMR revealed that the binding mode of NT fragment NT10-13 is heterogeneous. Epitope maps of NT10-13 at NTS ₁ suggested that tyrosine 11 (Y11) samples other conformations to those observed in crystal structures of NT-bound NTS ₁ . Molecular dynamics (MD) simulations confirmed that when NT is bound to NTS ₁ , residue Y11 can exist in two χ ₁ rotameric states, gauche plus (g ⁺ ) or gauche minus (g ^- ). Since only the g ⁺ Y11 state is observed in all the structures solved to date, we asked if the g ^- state is important for receptor activation. NT analogues with Y11 replaced with 7-OH-Tic were synthesized to restrain the dynamics of the side chain. P(OH-TIC)IL bound NTS ₁ with the same affinity as NT10-13 but did not activate NTS ₁ , instead acted as an antagonist. This study highlights that flexibility of Y11 in NT may be required for NT activation of NTS ₁ .
Competing Interests: The authors declare no competing financial interest.
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