PpiA, a Surface PPIase of the Cyclophilin Family in Lactococcus lactis

Background: Protein folding in the envelope is a crucial limiting step of protein export and secretion. In order to better understand this process in Lactococcus lactis, a lactic acid bacterium, genes encoding putative exported folding factors like Peptidyl Prolyl Isomerases (PPIases) were searched for in lactococcal genomes. Results: In L. lactis, a new putative membrane PPIase of the cyclophilin subfamily, PpiA, was identified and characterized. ppiA gene was found to be constitutively expressed under normal and stress (heat shock, H2O2) conditions. Under normal conditions, PpiA protein was synthesized and released from intact cells by an exogenously added protease, showing that it was exposed at the cell surface. No obvious phenotype could be associated to a ppiA mutant strain under several laboratory conditions including stress conditions, except a very low sensitivity to H2O2. Induction of a ppiA copy provided in trans had no effect i) on the thermosensitivity of an mutant strain deficient for the lactococcal surface protease HtrA and ii) on the secretion and stability on four exported proteins (a highly degraded hybrid protein and three heterologous secreted proteins) in an otherwise wild-type strain background. However, a recombinant soluble form of PpiA that had been produced and secreted in L. lactis and purified from a culture supernatant displayed both PPIase and chaperone activities. Conclusions: Although L. lactis PpiA, a protein produced and exposed at the cell surface under normal conditions, displaye

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry

p. 297–308The conditional solubility of scheelite CaWO 4 in molten NaCI--KC1 (1 : 1) has been studied either in oxobasic or oxoacidic media. In the former case it is increased by formation of sparingly soluble CaO according to: Ca 2+ + 02- ~ CaO(s), pK Ca° = 10800/T-- 5.8 (molality scale) In the later case, WO 2- behaves as an oxobase according to the following equilibria: WO42- ~- WO 3 (s) + 02_ pK 0 = 10.0 at 1000 K 3 WO2--¢- W30120+ 02_ pK 3 = 12.7 at 1000 K The latter equilibrium favours an increase in the W VI solubility when pO 2- is increased, for instance by injection of HC1. The whole set of results has been summarized by a conditional solubility diagram of scheelite versus pO 2-.Salvado