Hisano, T. | Search bioRxiv

bioRxiv2024

Loop modelling provides insights into regulation of mTORC1 activity via DEPTOR dimerisation

mTOR regulates cell growth by forming the mTORC1 and mTORC2 complexes. DEPTOR partially inhibits mTORC1, which in turn phosphorylates and inactivates it. Despite the mTORC1-DEPTOR structures, the exact mechanism remains unclear largely because functionally flexible key elements, DEPTORs linker in particular, are unresolved. By taking DEPTORs dimerisation into consideration, our modelling of these missing loops suggests that monomeric DEPTOR bound to mTORC1 in a non-inhibitory mode, while the domain-swapped dimeric DEPTOR could interact with mTORC1s FRB domain and block the kinases catalytic site with its linker. These two states indicate that linker phosphorylation inactivates DEPTOR possibly by disrupting its dimerisation, which could tether the linker to the kinase domain to enhance mTORC1 inhibition. In addition to DEPTOR, mTORs k9b-k10 loop, which harbours the S2481 autophosphorylation site, and mSIN1s flexible domains in mTORC2 might act as inhibitory elements too.

bioinformatics↗

bioRxiv2021

Unidirectional ion transport mechanism of a light-driven chloride pump revealed using X-ray free electron lasers

Light-driven chloride-pumping rhodopsins actively transport anions, including various halide ions, across cell membranes. Recent studies using time-resolved serial femtosecond crystallography (TR-SFX) have uncovered the structural changes and ion transfer mechanisms in light-driven cation-pumping rhodopsins. However, the mechanism by which the conformational changes pump an anion to achieve unidirectional ion transport, from the extracellular side to the cytoplasmic side, in anion-pumping rhodopsins remains enigmatic. We have collected TR-SFX data of Nonlabens marinus rhodopsin-3 (NM-R3), derived from a marine flavobacterium, at 10 s and 1 ms time-points after photoexcitation. Our structural analysis reveals the conformational alterations during ion transfer and after ion release. Movements of the retinal chromophore initially displace a conserved tryptophan to the cytoplasmic side of NM-R3, accompanied with a slight shift of the halide ion bound to the retinal. After ion release, the inward movements of helix C and helix G and the lateral displacements of the retinal block access to the extracellular side of NM-R3. Anomalous signal data have also been obtained from NM-R3 crystals containing iodide ions. The anomalous density maps provide insight into the halide binding site for ion transfer in NM-R3. SignificanceLight-driven chloride pumps have been identified in various species, including archaea and marine flavobacteria. The function of ion transportation controllable by light is utilized for optogenetics tools in neuroscience. Chloride pumps differ among species, in terms of amino acid homology and structural similarity. Our time-resolved crystallographic studies using X-ray free electron lasers reveal the molecular mechanism of halide ion transfer in a light-driven chloride pump from a marine flavobacterium. Our data indicate a common mechanism in chloride pumping rhodopsins, as compared to previous low temperature trapping studies of chloride pumps. These findings are significant not only for further improvements of optogenetic tools but also for a general understanding of the ion pumping mechanisms of microbial rhodopsins.

molecular biology↗