Neurotensin receptors are transmembrane receptors that bind the neurotransmitterneurotensin. Two of the receptors encoded by the NTSR1 and NTSR2 genes contain seven transmembrane helices and are G protein coupled. Numerous crystal structures have been reported for the neurotensin receptor 1 (NTS1). The third receptor has a single transmembrane domain and is encoded by the SORT1 gene.
Unusually for GPCRs, NTS1 can be expressed in an active form in the bacteria E. coli. It can be purified and analysed in vitro and has been analysed by a number of biophysical techniques such as surface plasmon resonance, FRET and cryo-electron microscopy.
Furthermore, high-resolution crystal structures have been determined for NTS1 in complex with the peptide full agonist NT8-13, non-peptide full agonist SRI-9829, partial agonist RTI-3a, antagonists / inverse agonists SR-48692 and SR-142948, as well as in the ligand-free state 
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^Attrill H, Harding PJ, Smith E, Ross S, Watts A (2009). "Improved yield of a ligand-binding GPCR expressed in E. coli for structural studies". Protein Expr Purif. 64 (1): 32–38. doi:10.1016/j.pep.2008.10.001. PMID18976711.