Abstract
Schizorhodopsins (SzRs) are light-driven inward proton pumps found in Asgard archaea, contrasting with most microbial rhodopsins that export protons. Some SzRs, including Methanoculleus taiwanensis SzR ( Mt SzR) and Methanoculleus sp. SzR ( M sSzR), exhibit remarkable heat tolerance, suggesting structural adaptations to extreme environments. Here, we report cryo-electron microscopy structures of Mt SzR and M sSzR at 2.4 and 2.7 Å resolutions, respectively, revealing distinct mechanisms for proton transport and thermostability. Both proteins share a cytoplasm-facing proton acceptor, yet Mt SzR employs a hydrophobic gating mechanism, whereas M sSzR lacks this barrier and stabilizes its acceptor through a salt-bridge network. Thermostability also diverges: Mt SzR relies on proline-rich loops and electrostatic interactions, while M sSzR achieves stability through reinforced trimerization and extensive interhelical aromatic packing. Structural and mutational analyses highlight the adaptability of SzRs and provide a framework for engineering robust photoreceptors for optogenetics and synthetic biology.
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Abstract
Schizorhodopsins (SzRs) are light-driven inward proton pumps found in Asgard archaea, contrasting with most microbial rhodopsins that export protons. Some SzRs, including Methanoculleus taiwanensis SzR (MtSzR) and Methanoculleus sp. SzR (MsSzR), exhibit remarkable heat tolerance, suggesting structural adaptations to extreme environments. Here, we report cryo-electron microscopy structures of MtSzR and MsSzR at 2.4 and 2.7 Å resolutions, respectively, revealing distinct mechanisms for proton transport and thermostability. Both proteins share a cytoplasm-facing proton acceptor, yet MtSzR employs a hydrophobic gating mechanism, whereas MsSzR lacks this barrier and stabilizes its acceptor through a salt-bridge network. Thermostability also diverges: MtSzR relies on proline-rich loops and electrostatic interactions, while MsSzR achieves stability through reinforced trimerization and extensive interhelical aromatic packing. Structural and mutational analyses highlight the adaptability of SzRs and provide a framework for engineering robust photoreceptors for optogenetics and synthetic biology.
Competing Interest Statement
The authors have declared no competing interest.
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