Type III secretion systems are essential virulence determinants for many gram-negative bacterial pathogens. MxiH is an extracellular alpha helical needle that is required for translocation of effector proteins into host cells [1]. Once inside, the effector proteins subvert normal cell function to aid infection. The needle protein F, polymerises to form a shaft [2,3,4].

1: Molecular model of a type III secretion system needle: Implications for host-cell sensing. Deane JE, Roversi P, Cordes FS, Johnson S, Kenjale R, Daniell S, Booy F, Picking WD, Picking WL, Blocker AJ, Lea SM; Proc Natl Acad Sci U S A. 2006;103:12529-12533. PMID:16888041

2: Structural characterization of the Yersinia pestis type III secretion system needle protein YscF in complex with its heterodimeric chaperone YscE/YscG. Sun P, Tropea JE, Austin BP, Cherry S, Waugh DS; J Mol Biol. 2008;377:819-830. PMID:18281060

3: The Pseudomonas aeruginosa type III secretion system has an exotoxin S/T/Y independent pathogenic role during acute lung infection. Galle M, Jin S, Bogaert P, Haegman M, Vandenabeele P, Beyaert R; PLoS One. 2012;7:e41547. PMID:22844497

4: Regulation of the Yersinia type III secretion system: traffic control. Dewoody RS, Merritt PM, Marketon MM; Front Cell Infect Microbiol. 2013;3:4. PMID:23390616