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

ABSTRACT: 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 (NTS₁). While several experimental structures show how NT binds NTS₁, details about the structural dynamics of NT during and after binding NTS₁, 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 NTS₁ suggested that tyrosine 11 (Y11) samples other conformations to those observed in crystal structures of NT-bound NTS₁. Molecular dynamics (MD) simulations confirmed that when NT is bound to NTS₁, residue Y11 can exist in two χ₁ 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 NTS₁ with the same affinity as NT10-13 but did not activate NTS₁, instead acted as an antagonist. This study highlights that flexibility of Y11 in NT may be required for NT activation of NTS₁.

SUBMITTER: Bumbak F

PROVIDER: S-EPMC7432660 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Cellular entry of nonenveloped and enveloped viruses is often accompanied by dramatic conformational changes within viral structural proteins. These rearrangements are triggered by a variety of mechanisms, such as low pH, virus-receptor interactions, and virus-host chaperone interactions. Reoviruses, a model system for entry of nonenveloped viruses, undergo a series of disassembly steps within the host endosome. One of these steps, infectious subviral particle (ISVP)-to-ISVP* conversion, is necessary for delivering the genome-containing viral core into host cells, but the physiological trigger that mediates ISVP-to-ISVP* conversion during cell entry is unknown. Structural studies of the reovirus membrane penetration protein, ?1, predict that interactions between ?1 and negatively charged lipid head groups may promote ISVP* formation; however, experimental evidence for this idea is lacking. Here, we show that the presence of polyanions (SO4(2-) and HPO4(2-)) or lipids in the form of liposomes facilitates ISVP-to-ISVP* conversion. The requirement for charged lipids appears to be selective, since phosphatidylcholine and phosphatidylethanolamine promoted ISVP* formation, whereas other lipids, such as sphingomyelin and sulfatide, either did not affect ISVP* formation or prevented ISVP* formation. Thus, our work provides evidence that interactions with membranes can function as a trigger for a nonenveloped virus to gain entry into host cells.Cell entry, a critical stage in the virus life cycle, concludes with the delivery of the viral genetic material across host membranes. Regulated structural transitions within nonenveloped and enveloped viruses are necessary for accomplishing this step; these conformational changes are predominantly triggered by low pH and/or interactions with host proteins. In this work, we describe a previously unknown trigger, interactions with lipid membranes, which can induce the structural rearrangements required for cell entry. This mechanism operates during entry of mammalian orthoreoviruses. We show that interactions between reovirus entry intermediates and lipid membranes devoid of host proteins promote conformational changes within the viral outer capsid that lead to membrane penetration. Thus, this work illustrates a novel strategy that nonenveloped viruses can use to gain access into cells and how viruses usurp disparate host factors to initiate infection.

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

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