Cryo-EM structure of the human MT1–Gi signaling complex

Hiroyuki H. Okamoto, Hirotake Miyauchi, Asuka Inoue, Francesco Raimondi, Hirokazu Tsujimoto, Tsukasa Kusakizako, Wataru Shihoya, Keitaro Yamashita, Ryoji Suno, Norimichi Nomura, Takuya Kobayashi, So Iwata, Tomohiro Nishizawa, Osamu Nureki

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


Melatonin receptors (MT1 and MT2) transduce inhibitory signaling by melatonin (N-acetyl-5-methoxytryptamine), which is associated with sleep induction and circadian rhythm modulation. Although recently reported crystal structures of ligand-bound MT1 and MT2 elucidated the basis of ligand entry and recognition, the ligand-induced MT1 rearrangement leading to Gi-coupling remains unclear. Here we report a cryo-EM structure of the human MT1–Gi signaling complex at 3.3 Å resolution, revealing melatonin-induced conformational changes propagated to the G-protein-coupling interface during activation. In contrast to other Gi-coupled receptors, MT1 exhibits a large outward movement of TM6, which is considered a specific feature of Gs-coupled receptors. Structural comparison of Gi and Gs complexes demonstrated conformational diversity of the C-terminal entry of the Gi protein, suggesting loose and variable interactions at the end of the α5 helix of Gi protein. These notions, together with our biochemical and computational analyses, highlight variable binding modes of Gαi and provide the basis for the selectivity of G-protein signaling.

Original languageEnglish
Pages (from-to)694-701
Number of pages8
JournalNature Structural and Molecular Biology
Issue number8
Publication statusPublished - 2021 Aug

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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