Needle length control and the secretion substrate specificity switch are only loosely coupled in the type III secretion apparatus of Shigella

Dakang Shen, Nao Moriya, Isabel Martinez-Argudo, Ariel J Blocker

Research output: Contribution to journalArticle (Academic Journal)peer-review

16 Citations (Scopus)


The type III secretion apparatus (T3SA), which is evolutionarily and structurally related to the bacterial flagellar hook basal body, is a key virulence factor used by many gram-negative bacteria to inject effector proteins into host cells. A hollow extracellular needle forms the injection conduit of the T3SA. Its length is tightly controlled to match specific structures at the bacterial and host-cell surfaces but how this occurs remains incompletely understood. The needle is topped by a tip complex, which senses the host cell and inserts as a translocation pore in the host membrane when secretion is activated. The interaction of two conserved proteins, inner-membrane Spa40 and secreted Spa32, respectively, in Shigella, is proposed to regulate needle length and to flick a type III secretion substrate specificity switch from needle components/Spa32 to translocator/effector substrates. We found that, as in T3SAs from other species, substitution N257A within the conserved cytoplasmic NPTH region in Spa40 prevented its autocleavage and substrate specificity switching. Yet, the spa40(N257A) mutant made only slightly longer needles with a few needle tip complexes, although it could not form translocation pores. On the other hand, Δspa32, which makes extremely long needles and also formed only few tip complexes, could still form some translocation pores, indicating that it could switch substrate specificity to some extent. Therefore, loss of needle length control and defects in secretion specificity switching are not tightly coupled in either a Δspa32 mutant or a spa40(N257A) mutant.
Original languageEnglish
Pages (from-to)1884-96
Number of pages13
Issue numberPt 7
Publication statusPublished - 2012

Bibliographical note

AJB and DKS designed the research. DSK, NM and IMA performed the research. All authors interpreted resulting data. DKS and AJB wrote the paper. Work was funded by MRC project grant G35208.


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