Type V secretion systems: an overview of passenger domain functions

Bacteria secrete proteins for different purposes such as communication, virulence functions, adhesion to surfaces, nutrient acquisition, or growth inhibition of competing bacteria. For secretion of proteins, Gram-negative bacteria have evolved different secretion systems, classified as secretion systems I through IX to date. While some of these systems consist of multiple proteins building a complex spanning the cell envelope, the type V secretion system, the subject of this review, is rather minimal. Proteins of the Type V secretion system are often called autotransporters (ATs). In the simplest case, a type V secretion system consists of only one polypeptide chain with a β-barrel translocator domain in the membrane, and an extracellular passenger or effector region. Depending on the exact domain architecture of the protein, type V secretion systems can be further separated into sub-groups termed type Va through e, and possibly another recently identified subtype termed Vf. While this classification works well when it comes to the architecture of the proteins, this is not the case for the function(s) of the secreted passenger. In this review, we will give an overview of the functions of the passengers of the different AT classes, shedding more light on the variety of functions carried out by type V secretion systems

A novel, proof-of-concept electrochemical impedimetric biosensor based on extracellular matrix protein–adhesin interaction

This work presents a novel perspective for electrochemical biosensors based on the detection of the interaction between extracellular matrix proteins and bacterial adhesins. Two types of impedimetric biosensors using collagen as a bioreceptor were investigated for their ability to detect pathogen adhesion using a well-characterised system of collagen-binding to recombinant E. coli expressing adhesin. First, a collagen–polymer-matrix-based biosensor was shown to detect whole bacteria in buffer media over the range 8 × 105 cfu to 8 × 107 cfu in a 10 μL sample. Second, a step-by-step full optimised biosensor based on direct collagen attachment showed bacterial detection over the range of 8 × 104 cfu to 8 × 107 cfu in a 10 μL sample. Electrochemical impedance spectroscopy and cyclic voltammetry were employed to assess the binding, which was corroborated by fluorescence binding assays. Up to now, a wide range of bioreceptors have been used in biosensor fabrication, including antibodies, oligonucleotides, phages and molecularly imprinted polymers. In this study, we show that extracellular matrix proteins can also be used for whole pathogen recognition by binding to adhesins

The Trimeric Autotransporter Adhesin YadA of Yersinia enterocolitica Serotype O:9 Binds Glycan Moieties

Yersinia adhesin A (YadA) is a key virulence factor of Yersinia enterocolitica and Yersinia pseudotuberculosis. YadA is a trimeric autotransporter adhesin, a class of adhesins that have been shown to enable many Gram-negative pathogens to adhere to/interact with the host extracellular matrix proteins such as collagen, vitronectin, and fibronectin. Here, we show for the first time that YadA of Yersinia enterocolitica serotype O:9 not only interacts with proteinaceous surface molecules but can also attach directly to glycan moieties. We show that YadA from Y. enterocolitica serotype O:9 does not interact with the vitronectin protein itself but exclusively with its N-linked glycans. We also show that YadA can target other glycan moieties as found in heparin, for example. So far, little is known about specific interactions between bacterial autotransporter adhesins and glycans. This could potentially lead to new antimicrobial treatment strategies, as well as diagnostic applications