Liquid-Liquid Phase Transition Drives Intra-chloroplast Cargo Sorting
In eukaryotic cells, organelle biogenesis is pivotal for cellular function and cell survival. Chloroplasts are unique organelles with a complex internal membrane network. The mechanisms of the migration of imported nuclear-encoded chloroplast proteins across the crowded stroma to thylakoid membranes...
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Published in | Cell Vol. 180; no. 6; pp. 1144 - 1159.e20 |
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Main Authors | , , , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
Elsevier Inc
19.03.2020
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Subjects | |
Online Access | Get full text |
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Summary: | In eukaryotic cells, organelle biogenesis is pivotal for cellular function and cell survival. Chloroplasts are unique organelles with a complex internal membrane network. The mechanisms of the migration of imported nuclear-encoded chloroplast proteins across the crowded stroma to thylakoid membranes are less understood. Here, we identified two Arabidopsis ankyrin-repeat proteins, STT1 and STT2, that specifically mediate sorting of chloroplast twin arginine translocation (cpTat) pathway proteins to thylakoid membranes. STT1 and STT2 form a unique hetero-dimer through interaction of their C-terminal ankyrin domains. Binding of cpTat substrate by N-terminal intrinsically disordered regions of STT complex induces liquid-liquid phase separation. The multivalent nature of STT oligomer is critical for phase separation. STT-Hcf106 interactions reverse phase separation and facilitate cargo targeting and translocation across thylakoid membranes. Thus, the formation of phase-separated droplets emerges as a novel mechanism of intra-chloroplast cargo sorting. Our findings highlight a conserved mechanism of phase separation in regulating organelle biogenesis.
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•A complex of STTs acts in sorting chloroplast Tat substrates to the thylakoids•Tat substrate activates the STT complex to undergo phase separation•Hcf106 reverses phase separation and facilitates cargo translocation
A pair of ankyrin repeat proteins in chloroplasts recognizes signal peptides on thylakoid-bound cargo proteins and undergoes liquid-liquid phase separation to facilitate their sorting and transport. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0092-8674 1097-4172 |
DOI: | 10.1016/j.cell.2020.02.045 |