Characterization of the Modular Design of the Autolysin/Adhesin Aaa from Staphylococcus Aureus

BACKGROUND: Staphylococcus aureus is a frequent cause of serious and life-threatening infections, such as endocarditis, osteomyelitis, pneumonia, and sepsis. Its adherence to various host structures is crucial for the establishment of diseases. Adherence may be mediated by a variety of adhesins, among them the autolysin/adhesins Atl and Aaa. Aaa is composed of three N-terminal repeated sequences homologous to a lysin motif (LysM) that can confer cell wall attachment and a C-terminally located cysteine, histidine-dependent amidohydrolase/peptidase (CHAP) domain having bacteriolytic activity in many proteins. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show by surface plasmon resonance that the LysM domain binds to fibrinogen, fibronectin, and vitronectin respresenting a novel adhesive function for this domain. Moreover, we demonstrated that the CHAP domain not only mediates the bacteriolytic activity, but also adherence to fibrinogen, fibronectin, and vitronectin, thus demonstrating for the first time an adhesive function for this domain. Adherence of an S. aureus aaa mutant and the complemented aaa mutant is slightly decreased and increased, respectively, to vitronectin, but not to fibrinogen and fibronectin, which might at least in part result from an increased expression of atl in the aaa mutant. Furthermore, an S. aureus atl mutant that showed enhanced adherence to fibrinogen, fibronectin, and endothelial cells also demonstrated increased aaa expression and production of Aaa. Thus, the redundant functions of Aaa and Atl might at least in part be interchangeable. Lastly, RT-PCR and zymographic analysis revealed that aaa is negatively regulated by the global virulence gene regulators agr and SarA. CONCLUSIONS/SIGNIFICANCE: We identified novel functions for two widely distributed protein domains, LysM and CHAP, i.e. the adherence to the extracellular matrix proteins fibrinogen, fibronectin, and vitronectin. The adhesive properties of Aaa might promote S. aureus colonization of host extracellular matrix and tissue, suggesting a role for Aaa in the pathogenesis of S. aureus infections

Chemical composition and antibacterial activity of red murta (Ugni molinae Turcz.) seeds: an undervalued Chilean resource

Murta (Ugni molinae Turcz) is an endemic Chilean specie mostly used in medical, cosmetic, and food industries. However, during the industrial processing of murta fruits, the biomass containing the seeds is discarded as an industrial byproduct that does not find significant uses yet. This work is a first approach to valorize murta biomass through the identification and quantification of principal chemical constituents and exploring their antibacterial properties. The proximal analysis revealed that murta seeds exhibited significant content of raw fiber (64%), crude fat (14%), crude protein (12%), and low levels of ashes (1.5%) and minerals (0.04-0.23%). Dietary fiber was mainly composed of lignin, cellulose, pectin, and hemicellulose. Polyunsaturated fatty acids (89.0%), monounsaturated fatty acids (7.7%), and saturated fatty acids (3.3%) were the main constituents of seed oils. The arginine, asparagine, glutamic acid, and glycine were the primary protein constituent amino acids. Tannin fractions, total polyphenolic content, and oxygen radical absorbance capacity as antioxidant activity were measured. The chromatographic and mass spectrometric analysis (HPLC-MS/MS) confirmed the presence of several phenolic compounds like phenolic acids, flavonols, flavones, proanthocyanidins, and high molecular weight polyphenols. The murta seed extract showed high antibacterial activity against both Gram positive (Staphylococcus aureus, Bacillus cereus, and Streptococcus pyogenes) and Gram negative (Escherichia coli, Salmonella typhi, and Pseudomonas aeruginosa) bacterial strains. Murta seeds could be considered as a new source of nutritional components and bioactive compounds for different nutraceutical and food applications.Grant CONICYT PIA/APOYO CCTE FB17000