Crystal structure of the outer membrane protein RcsF, a new substrate for the periplasmic protein- XXXX isomerase DsbC.

@entity462 @entity3793 @entity2569 @entity920 @entity1520 @entity1525
The bacterial Rcs phosphorelay is a stress-induced defense mechanism that controls the expression of numerous genes, including those for capsular polysaccharides, motility, and virulence factors. It is a complex multicomponent system that includes the @entity3793 kinase (RcsC) and the response regulator (RcsB) and also auxiliary proteins such as RcsF. RcsF is an outer membrane lipoprotein that transmits signals from the cell surface to RcsC. The physiological signals that activate RcsF and how RcsF interacts with RcsC remain unknown. Here, we report the three-dimensional structure of RcsF. The fold of the protein is characterized by the presence of a central 4-stranded b sheet, which is conserved in several other proteins, including the @entity920 -binding domain of the amyloid precursor protein. RcsF, which contains four conserved @entity462 residues, presents two nonconsecutive @entity1525 between @entity2569 (74) and @entity2569 (118) and between @entity2569 (109) and @entity2569 (124), respectively. These two @entity1525 are not functionally equivalent; the @entity2569 (109)- @entity2569 (124) @entity1520 is particularly important for the assembly of an active RcsF. Moreover, we show that formation of the nonconsecutive @entity1525 of RcsF depends on the periplasmic @entity1520 isomerase DsbC. We trapped RcsF in a mixed @entity1520 complex with DsbC, and we show that deletion of dsbC prevents the activation of the Rcs phosphorelay by signals that function through RcsF. The three-dimensional structure of RcsF provides the structural basis to understand how this protein triggers the Rcs signaling cascade.
