a b s t r a c tA new Staphylococcus xylosus strain was isolated. The extracellular lipase of S. xylosus (wt-SXL2) was purified to homogeneity from the culture medium. The specific activity of the purified enzyme, measured at pH 8.5 and 55• C using tributyrin or olive oil emulsion, reached, respectively, 6300 U/mg or 2850 U/mg. The sequenced 18 N-terminal amino acid showed a high degree of identity with known staphylococcal lipase sequences.The gene encoding the mature lipase was cloned and sequenced. The deduced amino acid sequence showed a significant similarity with various staphylococcal lipases. The highest overall identity (98.74%) was found with S. xylosus lipase (SXL1). The mature part of the lipase was expressed in Escherichia coli. The recombinant lipase was purified by affinity chromatography. The specific activity of the recombinant lipase was 4100 or 1500 U/mg using tributyrin or olive oil emulsion as substrate, respectively, at pH 8.5 and 55• C. The wild type and recombinant lipases presented a quite interesting thermal stability, after an incubation of 60 min at 55• C and they are found to be highly stable at a pH ranging from 4 to 11. Due to its stability at high temperature and in organic solvent, the wt-SXL2 was used as biocatalyst to synthesise a high added value molecules.

The majority of proteases are synthesized in an inactive form, termed zymogen, which consists of a propeptide and a protease domain. The propeptide is commonly involved in the correct folding and specific inhibition of the enzyme. The propeptide of the house dust mite allergen Der p 3, NPILPASPNAT, contains a proline-rich motif (PRM), which is unusual for a trypsin-like protease. By truncating the propeptide or replacing one or all of the prolines in the non-glycosylated zymogen with alanine(s), we demonstrated that the full-length propeptide is not required for correct folding and thermal stability and that the PRM is important for the resistance of proDer p 3 to undesired proteolysis when the protein is expressed in Pichia pastoris. Additionally, we followed the maturation time course of proDer p 3 by coupling a quenched-flow assay to mass spectrometry analysis. This approach allowed to monitor the evolution of the different species and to determine the steady-state kinetic parameters for activation of the zymogen by the major allergen Der p 1. This experiment demonstrated that prolines 5 and 8 are crucial for proDer p 3-Der p 1 interaction and for activation of the zymogen.

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rDer p 3-S196A should be used for the diagnosis of HDM allergy elicited by Der p 3, and proDer p 3 may represent a hypoallergen of Der p 3.

a b s t r a c tThe ability of a non-commercial immobilized Staphylococcus xylosus lipase to catalyze the esterification of propanol with gallic acid was investigated and the antioxidant as well as the antimicrobial activities of the ester formed were evaluated. The response surface methodology, based on a three variables Box-Behnken design (reaction temperature, enzyme amount and 1-propanol/gallic acid molar ratio), was used to optimize the experimental conditions of propylgallate synthesis. The maximum conversion yield (90% ±3.5) was obtained by using 400 IU of immobilized lipase and a propanol/gallic acid at a molar ratio of 160 at 52 • C. The obtained ester was characterized by spectroscopic methods, NMR and FTIR. The antioxidant activity of propyl gallate was evaluated and compared to the synthetic classical antioxidants, BHA and ascorbic acid, taken as references. In addition, the antimicrobial activity of the propyl gallate was tested against S. xylosus, Escherchia coli and Staphylococcus aureus using disc diffusion and macrodilution methods. Our results show that the synthesized propyl gallate ester presents a higher antioxidant and antimicrobial power than the parent gallic acid as well as the synthetic classical antioxidants.