Dorgan, B. | bioRxiv Science

bioRxiv2021

Molecular and cellular insight into Escherichia coli SslE and its role during biofilm maturation

Escherichia coli is a Gram-negative bacterium that colonizes the human intestine and virulent strains can cause severe diarrhoeal and extraintestinal diseases. The protein SslE is secreted by a range of pathogenic and some commensal E. coli strains. It can degrade mucins in the intestine, promotes biofilm maturation and it is a major determinant of infection in virulent strains, although how it carries out these functions is not well understood. Here we examine SslE from the E. coli Waksman and H10407 strains and reveal that it has a novel and dynamic structure. In response to acidification within mature biofilms we show how SslE forms a unique functional aggregate that interacts with cellulose and regulates the distribution of exopolysaccharides in macrocolony biofilms. Our data indicates that the spatial organization of SslE polymers and local pH are critical for biofilm maturation and SslE is a key factor that drives persistence of SslE-secreting bacteria during acidic stress.

microbiology↗

bioRxiv2019

Structure and functional analysis of the Legionella chitinase ChiA reveals a novel mechanism of metal-dependent mucin degradation

Chitinases are important enzymes that contribute to the generation of carbon and nitrogen from chitin, a long chain polymer of N-acetylglucosamine that is abundant in insects, fungi, invertebrates and fish. Although mammals do not produce chitin, chitinases have been identified in bacteria that are key virulence factors in severe respiratory, gastrointestinal and urinary diseases. However, it is unclear how these enzymes are able to carry out this dual function. Legionella pneumophila is the causative agent of Legionnaires disease, an often-fatal pneumonia and its chitinase ChiA is essential for the survival of L. pneumophila in the lung. Here we report the first atomic resolution insight into the pathogenic mechanism of a bacterial chitinase. We derive an experimental model of intact ChiA and show how its N-terminal region targets ChiA to the bacterial surface after its secretion. We provide the first evidence that L. pneumophila can bind mucins on its surface but this is not dependent on chiA. This demonstrates that additional peripheral mucin binding proteins are also expressed in L. pneumophila. Finally, we show that the ChiA C-terminal chitinase domain has novel metal-dependent peptidase activity against mammalian mucins. These findings suggest that ChiA facilitates bacterial penetration of the alveolar mucosa and ChiA may be a promising target for vaccine development.

microbiology↗