Cryo-EM structure of the SRI-HtrI complex reveals the cytoplasmic coupling in an archaeal phototaxis system
Journal
Nature Communications
Journal Volume
17
Journal Issue
1
Start Page
Article number: 5306
ISSN
2041-1723
Date Issued
2026-04-16
Author(s)
Abstract
Sensory rhodopsins (SRs) in haloarchaea form complexes with their cognate transducers (Htrs) to produce wavelength-specific phototactic responses, yet similar architectures mediate distinct behaviors: SRI mediates attraction, SRII drives repulsion, whereas SRM modulates both responses. Until now, structural insight was limited to the Natronomonas pharaonis SRII-HtrII system in a truncated form, without a full-length counterpart for comparison. Moreover, NpHtrII is distinct among HtrII transducers in lacking the large periplasmic domain retained in homologs from Halobacterium salinarum, Haloarcula marismortui and Haloarcula taiwanensis, leaving the canonical SR-Htr architecture unknown. Here, we report the cryo-EM structure of the Haloarcula taiwanensis SRI-HtrI complex, providing a near native, non-crystallized view of a full-length SR-Htr dimer with the cytoplasmic HAMP1 domain resolved. The structure reveals the intact homodimeric receptor-transducer assembly and visualizes the interface between the helix G (Arg215), SRI E-F loop (Pro154), and HtrI HAMP1. These findings fill the long-standing structural gap for a canonical SR-Htr complex and establish a framework for conserved receptor-transducer coupling across archaeal phototaxis systems.
Publisher
Springer Science and Business Media LLC
Type
journal article