Structural studies of surface adhesins expressed by oral bacteria

Dental plaque is one of the most complex biofilms known and consists of hundreds of bacterial species. Plaque development is initiated by the attachment of salivary proteins to the tooth surface, followed by adherence of early colonizers, such as the Gram-positive Actinomyces oris and oral streptococci. These bacteria form an initial biofilm that is used as attachment surface for late colonizers. The key factors for these microorganisms to network with other bacteria and cells are their surface adhesins and pili. These Gram-positive surface proteins are assembled by very different mechanisms. One form represents the pili, that consists of polymerized proteins linked by covalent bonds with a large adhesin located at the tip. A second form consists of large monomeric proteins with N-terminal adhesive domains presented on stalks formed by repetitive small domains. A third form is represented by the antigen I/II proteins, expressed by oral streptococci. Antigen I/II have a unique fold where a central domain is presented on a stalk formed by intertwining flanking regions bringing both the N- and C-termini close to the cell wall. We have solved structures representing all three aforementioned groups; the pilin protein FimP from A. oris, the surface adhesin sgo0707 from Streptococcus gordonii and antigen I/II proteins from S. gordonii, Streptococcus mutans as well as from Streptococcus pyogenes. The late colonizers are often Gram-negative and one of these bacteria is the periodontal pathogen Porphyromonas gingivalis. This bacteria causes tooth loss and chronic inflammation and increasing evidence points to that P. gingivalis also is involved in the onset of disease at non-oral sites, causing cancer, cardiovascular disease and diabetes. This bacteria expresses two forms of pili with hitherto unexplored structures. Since these pili are important virulence factors we are focusing on structure determination also of these.

Large-Scale Computational Screening of Novel Compounds for Carbon Capture

Carbon capture and storage (CCS) applications offer a plausible solution to the urgent need for a carbon neutral energy source from stationary sources, including power plants and industrial processes. The most mature technology for post-combustion capture currently uses a liquid sorbent, amine scrubbing. However, with the existing technology, a large amount of heat is required for the regeneration of the liquid sorbent, which introduces a substantial energy penalty. Operation at higher temperatures could reduce this energy penalty by allowing the integration of waste heat back into the power cycle. New solid absorbents for use at intermediate to high temperatures, such as CaO, have shown promise in pilot plant studies, but are still far from ideal due to their poor capacity retention upon successive cycling. This presentation will describe our studies aimed at rationally selecting and designing materials for carbon capture and storage applications. We use ab initio calculations of oxide materials from the Materials Project database1 in an effort to screen for novel materials with optimal thermodynamic and kinetic properties for CO2 looping applications. From the determination of a material's optimised structure and ground state energy we have then constructed a screening routine for materials within the database based on simulating their carbonation equilibria and phase stability under differing atmospheric concentrations of CO2. A number of promising materials were identified from the screening, and we are currently investigating their properties experimentally, by using a combination of methods (including thermogravimetric analysis, in situ x-ray diffraction and microscopy). In this way we are able to assess the validity of the screening methodology, and use the insights afforded by experimental studies to iteratively improve the entire process.