A novel stabilization mechanism for the type VI secretion system sheath

The type VI secretion system (T6SS) is a phage-derived contractile nanomachine primarily involved in interbacterial competition. Its pivotal component, TssA, is indispensable for the assembly of the T6SS sheath structure, the contraction of which propels a payload of effector proteins into neighbori...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2021-02, Vol.118 (7), p.1-9
Main Authors: Bernal, Patricia, Furniss, R. Christopher D., Fecht, Selina, Leung, Rhoda C. Y., Spiga, Livia, Mavridou, Despoina A. I., Filloux, Alain
Format: Article
Language:English
Subjects:
Biological Sciences
Protein Stability
Pseudomonas - metabolism
Pseudomonas - ultrastructure
Type VI Secretion Systems - chemistry
Type VI Secretion Systems - metabolism
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Summary:The type VI secretion system (T6SS) is a phage-derived contractile nanomachine primarily involved in interbacterial competition. Its pivotal component, TssA, is indispensable for the assembly of the T6SS sheath structure, the contraction of which propels a payload of effector proteins into neighboring cells. Despite their key function, TssA proteins exhibit unexpected diversity and exist in two major forms, a short form (TssAS) and a long form (TssAL). While TssAL proteins interact with a partner, called TagA, to anchor the distal end of the extended sheath, the mechanism for the stabilization of TssAS-containing T6SSs remains unknown. Here we discover a class of structural components that interact with short TssA proteins and contribute to T6SS assembly by stabilizing the polymerizing sheath from the baseplate. We demonstrate that the presence of these components is important for full sheath extension and optimal firing. Moreover, we show that the pairing of each form of TssA with a different class of sheath stabilization proteins results in T6SS apparatuses that either reside in the cell for some time or fire immediately after sheath extension. We propose that this diversity in firing dynamics could contribute to the specialization of the T6SS to suit bacterial lifestyles in diverse environmental niches.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2008500118