Crystal structure of secretory protein Hcp3 from Pseudomonas aeruginosa
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The Type VI secretion pathway transports proteins across the cell envelope of Gram-negative bacteria. Pseudomonas aeruginosa, an opportunistic Gram-negative bacterial pathogen infecting humans, uses the type VI secretion pathway to export specific effector proteins crucial for its pathogenesis. The HSI-I virulence locus encodes for several proteins that has been proposed to participate in protein transport including the Hcp1 protein, which forms hexameric rings that assemble into nanotubes in vitro. Two Hcp1 paralogues have been identified in the P. aeruginosa genome, Hsp2 and Hcp3. Here, we present the structure of the Hcp3 protein from P. aeruginosa. The overall structure of the monomer resembles Hcp1 despite the lack of amino-acid sequence similarity between the two proteins. The monomers assemble into hexamers similar to Hcp1. However, instead of forming nanotubes in head-to-tail mode like Hcp1, Hcp3 stacks its rings in head-to-head mode forming double-ring structures.
KeywordsType VI (T6SS) secretion system Hcp3 Hcp1 X-ray crystallography Structural genomics
Type VI secretion system
Protein Data Bank
Single-wavelength anomalous diffraction
Root mean square deviation
We thank all members of the Structural Biology Center at Argonne National Laboratory and at the Ontario Centre for Structural Proteomics for their help in conducting these experiments. This work was supported by National Institutes of Health grant GM074942 and by the U.S. Department of Energy, Office of Biological and Environmental Research, under contract DE-AC02-06CH11357 and by the US National Science Foundation grant MCB 0231319 (to R.H.W.), and by Genome Canada (through the Ontario Genomics Institute).
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