The Salmonella type III secretion system inner rod protein PrgJ is partially folded.
The type III secretion system (T3SS) is essential in the pathogenesis of many bacteria. The inner rod is important in the assembly of the T3SS needle complex. However, the atomic structure of the inner rod protein is currently unknown. Based on computational methods, others have suggested that the Salmonella inner rod protein PrgJ is highly helical, forming a folded 3 helix structure. Here we show by CD and NMR spectroscopy that the monomeric form of PrgJ lacks a tertiary structure, and the only well-structured part of PrgJ is a short α-helix at the C-terminal region from residues 65-82. Disruption of this helix by glycine or proline mutation resulted in defective assembly of the needle complex, rendering bacteria incapable of secreting effector proteins. Likewise, CD and NMR data for the Shigella inner rod protein MxiI indicate this protein lacks a tertiary structure as well. Our results reveal that the monomeric forms of the T3SS inner rod proteins are partially folded.
Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045, USA.
Dalian
D
Zhong
Matthew
M
Lefebre
Kawaljit
K
Kaur
Melanie A
MA
McDowell
Courtney
C
Gdowski
Sunhwan
S
Jo
Yu
Y
Wang
Stephen H
SH
Benedict
Susan M
SM
Lea
Jorge E
JE
Galan
Roberto N
RN
De Guzman
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000502:physiology*; D002942:Circular Dichroism; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems