A model built that is based on the "molecular snapshot" of pilus assembly at the bacterial outer membrane by the twin pores usher complex.
David G. Thanassi, PhD, and co-investigators from
The investigators used X-ray crystallography to determine the structure of a protein – called the usher – that is part of the chaperone/usher pathway and serves as a molecular scaffold for the assembly of adhesive pili by pathogenic bacteria such as E. coli. Pili are hair-like fibers that form a class of virulence factors that allow bacteria to attach to host cells and cause disease.
In addition to the crystal structure analysis of the usher, the researchers used electron microscopy imaging to capture a “molecular snapshot” of the pilus fiber during the act of secretion through the usher to the cell surface. These structures show the pilus assembly machinery in action during the bacterial outer membrane translocation process. The usher contains two channels or “twin pores.”
Thanassi said the team discovered that only one of these pores is used for secretion while the other remains closed. This discovery – and others the team anticipates to find – provides insight into the secretion of virulence factors across the outer membrane of Gram-negative bacteria.
“This ‘molecular snapshot’ is a new way to look at and analyze virulence factors assembled by bacteria,” says Thanassi, of the
Additional findings are detailed in the Cell article, titled “Fiber Formation across the Bacterial Outer Membrane by the Chaperone/Usher Pathway.” In an accompanying commentary to the article in the journal, scientists from the Swedish Institute for Infectious Disease Control and the Karolinska Institute in