2UWJ: Structure of the Heterotrimeric Complex Which Regulates Type III Secretion Needle Formation

Type III secretion systems (T3SS), found in several Gram-negative pathogens, are nanomachines involved in the transport of virulence effectors directly into the cytoplasm of target cells. T3SS are essentially composed of basal membrane-embedded ring-like structures and a hollow needle formed by a single polymerized protein. Within the bacterial cytoplasm, the T3SS needle protein requires two distinct chaperones for stabilization before its secretion, without which the entire T3SS is nonfunctional. The 2.0-A x-ray crystal structure of the PscE-PscF(55-85)-PscG heterotrimeric complex from Pseudomonas aeruginosa reveals that the C terminus of the needle protein PscF is engulfed within the hydrophobic groove of the tetratricopeptide-like molecule PscG, indicating that the macromolecular scaffold necessary to stabilize the T3SS needle is totally distinct from chaperoned complexes between pilus- or flagellum-forming molecules. Disruption of specific PscG-PscF interactions leads to impairment of bacterial cytotoxicity toward macrophages, indicating that this essential heterotrimer, which possesses homologs in a wide variety of pathogens, is a unique attractive target for the development of novel antibacterials.
PDB ID: 2UWJDownload
MMDB ID: 46796
PDB Deposition Date: 2007/3/22
Updated in MMDB: 2012/11 
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 2UWJ: hexameric; determined by author and by software (PQS)
Molecular Components in 2UWJ
Label Count Molecule
Proteins (6 molecules)
Type III Export Protein Psce
Molecule annotation
Type III Export Protein Pscf
Molecule annotation
Type III Export Protein Pscg
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB