sctF1
Domain
Deletion of the last five residues prevents self-association and yields monomeric proteins that allow biophysical studies (PubMed:16501225, PubMed:17617421). Forms a right-handed helical assembly with roughly 11 subunits per two turns (PubMed:22699623, PubMed:30242280). The location of the negatively charged surfaces are radically different among the needle filament proteins PrgI, BsaL and MxiH (PubMed:17617421). In PrgI, the major negatively charged surface is not on the 'face' but instead is on the 'side' of the two-helix bundle, and only residues from helix alpha1 contribute to this negative region (PubMed:17617421). The insertion of the needle tip complex on the distal end of the filament results in significant conformational changes in PrgI/SctF (PubMed:34706941).
Function
Component of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:12754250, PubMed:16501225, PubMed:30242280, PubMed:33750771). PrgI/SctF1 forms the external needle filament that protrudes from the bacterial surface (PubMed:12754250, PubMed:16501225, PubMed:22699623, PubMed:30242280, PubMed:31260457, PubMed:33750771). Is probably involved in the transduction of an activating signal, thought to be mediated by the distal tip of the needle filament, to the secretion machine (PubMed:31260457). Required for invasion of epithelial cells (PubMed:17617421). Required for the secretion of the effector protein SptP (PubMed:31260457, PubMed:33750771).
During infection, can induce innate immune responses (PubMed:24643544). The needle proteins interact with host TLR2 or TLR4, and induce signaling by NF-kappa-B and/or AP-1 (PubMed:24643544). This activation is MyD88 dependent and results in increased expression of cytokines, including TNF-alpha, IL-6 and IL-8 (PubMed:24643544).
Sequence Similarities
Belongs to the SctF family.
Cellular localization
- Secreted
- Cell surface
Alternative names
prgI, STM2873, sctF1, SPI-1 type 3 secretion system needle filament protein, T3SS-1 needle filament protein