4XMR:
reference: Structural basis for amino-acid recognition and transmembrane signalling by tandem Per-Arnt-Sim (tandem PAS) chemoreceptor sensory domains., Liu YC, Machuca MA, Beckham SA, Gunzburg MJ, Roujeinikova A, Acta Crystallogr D Biol Crystallogr. 2015 Oct;71(Pt 10):2127-36. doi:, 10.1107/S139900471501384X. Epub 2015 Sep 30. PMID: 26457436

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