TRIMBAT

Trimeric Bacterial Autotransporters

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 Obiettivo del progetto (Objective)

'Bacterial adhesins play a crucial role in pathogen-host interactions, initiating infections by adhesion to the extracellular matrix and to cell surface proteins prior to invasion. A family of non-fimbrial adhesins, the trimeric autotransporter adhesins (TAAs), has recently been described in gram-negative pathogens. The common biological role of all these TAAs is to mediate the interaction of pathogenic bacteria with their hosts. There is an increasing body of evidence that TAAs represent highly important bacterial pathogenicity factors. Typically TAAs are long, fibrous proteins. They are constructed of a set of repetitive modules or domains that are combined in a fashion of building blocks to meet the individual needs of the pathogen. There is detailed structural and functional information for only a few TAA domains at present. The head domain structure of YadA from Yersinia enterocolitica was solved in Goldman group and motifs were identified that contribute to collagen binding. YadA is an autotransporter, with a globular head, a coiled coil stalk and a C-terminal membrane anchor/translocator. The aim of the proposed project is to: 1. Understand how the β-barrel translolates the passenger domain. 2. Understand the folding mechanism of the β-barrel. 3. Determine the structure of the YadA transmembrane domain in complex with with a collagen peptides.'

Introduzione (Teaser)

Pathogenic bacteria possess a full arsenal of weapons against the cells they invade. One of the most potent and crucial for initiation of an infection is that of being able to stick to the host's cell surface proteins.

Descrizione progetto (Article)

The molecules responsible for this coup are called adhesins. Research has recently uncovered a new family, the trimeric autotransporter adhesins (TAAs), in gram-negative bacteria. This group of bacteria includes many pathogens including Escherichia coli and other gut-inhabiting microbes.

The molecular organisation of TAAs follows some surprisingly simple basic building rules. They have a head and a stalk made of building blocks that can be varied and repeated, probably evolved to confer a specific fit with the host.

The aim of the recently completed European 'Trimeric Bacterial Autotransporters' (Trimbat) project was to investigate the structure and biochemistry of the TAA family. As the formation of a secure landing and adhesion platform is key to a successful invasion, intricate knowledge of their initiation and building structure would be important for drugs and vaccines to stem infection.

The Trimbat team first selected a base containing the YadA protein, and four different stalk lengths. In line with the modular nature of the invasion platform, they then chose a variety of heads including the so-called Cherry-tag and maltose-binding protein (MBP).

The researchers successfully designed and expressed hybrid TAAs for in vivo studies of the mechanism and structures involved. Also, by engineering MBP, the folding rate of the protein was slowed down, rendering the YadA head domain larger than normal in the bacteria's extracellular space, which made study of its structure easier.

Once the structure of TAAs is fully understood, the next step is to design drugs and vaccines that have the configuration to prevent adhesion to the host and therefore stop the first steps of colonisation. The alternative is to use engineered super-adhesives where needed, perhaps to anchor beneficial bacteria.