001. A significantly decreased lipase activity was detected after 24 h incubation with LasB in the absence of alginate (p = 7.9 × 10-6). In contrast, no activity was lost in the presence of alginate. Moreover, the experiment again clearly showed that the addition of alginate did not MK-0518 supplier stimulate the lipase activity, since the activity was similar in presence and absence of alginate. A stimulation of lipase activity would be a hint on conformational

changes of the lipase protein. However, this seemed not to be happened. Lipase activity was found similar in the presence and in the absence of alginate without proteolytic treatment. Furthermore, no interfacial activation of the lipase was observed. This was expected as discussed above. However, elastase activity measured selleck products Thiazovivin manufacturer at the end of the experiment revealed constant

over time. These results led to the suggestions that i) LasB is able to degrade the lipase LipA and ii) alginate protects the lipase molecule from degradation, possibly by covering of cleavage sites. Elastase LasB has been described as one of the major extracellular proteases of P. aeruginosa[2]. The influence of LasB on the biofilm structure of mucoid P. aeruginosa was shown recently [1]. It was hypothesized that the proteolytic degradation of extracellular proteins mediated by LasB changes the physico-chemical properties of the EPS of P. aeruginosa and thereby, influences the structure of the biofilm [1]. Accordingly, a post-translational degradation of extracellular proteins during P. aeruginosa biofilm maturation was shown by proteome analysis [55].

Thereby, LasB has been identified as one of the enzymes involved [56]. Post-translational proteolytic processing cascades of extracellular proteins have also been found in other organisms [57, 58]. Modeling of interaction between lipase and polysaccharide alginate Molecular modeling of inter- and intramolecular interactions between the extracellular lipase LipA and the exopolysaccharide alginate from P. aeruginosa was performed by molecular mechanics force field approach using a minimized energy simulation strategy Rutecarpine (Figure 6). The crystal structure of the extracellular lipase LipA from P. aeruginosa[37] and a section of an alginate molecule were used. The modeling was carried out in presence and absence of water showing similar results. The calculations revealed that the interaction between lipase and alginate is mainly based on electrostatic interactions between negatively charged carboxyl groups of the polysaccharide and the positively charged amino acids of the protein as arginine, lysine and histidine (Figure 6, shown in blue). Mainly arginine, which is positively charged by the guanidinium group formed dominant interactions with the alginate chain. In accordance, the interaction remained stable even in the presence of water, whereas the histidine- and lysine-alginate interactions were slightly weakened.