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Publication Abstract from PubMed

The Type 3 Secretion System (T3SS) and the bacterial flagellum are related pathogenicity associated appendages found at the surface of many disease-causing bacteria. These appendages consist of long tubular structures that protrude away from the bacterial surface, to interact with the host cell and/or promote motility. A proposed "ruler" protein tightly regulates the length of both the T3SS and the flagellum, but the molecular basis for this length control has remained poorly characterized and controversial. Using the Pseudomonas aeruginosa T3SS as a model system, we report the first structure of a T3SS ruler protein, revealing a "ball-and-chain" architecture, with a globular C-terminal domain (the ball) preceded by a long intrinsically disordered N-terminal polypeptide chain. The dimensions and stability of the globular domain does not support its potential passage through the inner lumen of the T3SS needle. We further demonstrate that a conserved motif at the Nterminus of the ruler protein interacts with the T3SS autoprotease in the cytosolic side. Collectively, these data suggest a potential mechanism for needle length sensing by ruler proteins, whereby upon T3SS needle assembly the ruler protein's N-terminal end is anchored on the cytosolic side, with the globular domain located on the extracellular end of the growing needle. Sequence analysis of T3SS and flagellar ruler proteins show that this mechanism is likely conserved across systems.

The Structure of a T3SS Ruler Protein Suggests a Molecular Mechanism for Needle Length Sensing.,Bergeron JR, Fernandez L, Wasney GA, Vuckovic M, Reffuveille F, Hancock RE, Strynadka NC J Biol Chem. 2015 Nov 20. pii: jbc.M115.684423. PMID:26589798^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.