Frenken L G, de Groot A, Tommassen J, Verrips C T
Unilever Research Laboratorium, Vlaardingen, The Netherlands.
Mol Microbiol. 1993 Aug;9(3):591-9. doi: 10.1111/j.1365-2958.1993.tb01719.x.
The LipB protein of Pseudomonas glumae is essential for the production of active extracellular lipase encoded by the lipA gene. When lipase is overproduced in P. glumae in the absence of a functional lipB gene, the enzyme accumulates intracellularly in an inactive conformation. Heterologous expression of the lipase in Pseudomonas aeruginosa, Bacillus subtilis and Escherichia coli indicated that LipB is not directly involved in the translocation of the lipase across the inner or outer membrane. However, the presence of LipB was essential for obtaining active lipase and had a profound influence on the stability of the protein to proteolytic degradation. Inactive lipase, produced in the absence of LipB could be activated in vitro by unfolding and refolding, which demonstrates that LipB activity is not responsible for an essential covalent modification of the enzyme. We propose that LipB is a lipase-specific foldase. Furthermore, proper folding of the lipase in the periplasm appears to be essential for Xcp-mediated translocation across the outer membrane.
水稻细菌性条斑病菌的LipB蛋白对于由lipA基因编码的活性胞外脂肪酶的产生至关重要。当在缺乏功能性lipB基因的情况下，脂肪酶在水稻细菌性条斑病菌中过量产生时，该酶以无活性构象在细胞内积累。脂肪酶在铜绿假单胞菌、枯草芽孢杆菌和大肠杆菌中的异源表达表明，LipB并不直接参与脂肪酶跨内膜或外膜的转运。然而，LipB的存在对于获得活性脂肪酶至关重要，并且对蛋白质对蛋白水解降解的稳定性有深远影响。在没有LipB的情况下产生的无活性脂肪酶可以通过体外展开和重折叠而被激活，这表明LipB的活性并不负责对该酶进行必要的共价修饰。我们提出LipB是一种脂肪酶特异性折叠酶。此外，周质中脂肪酶的正确折叠似乎对于Xcp介导的跨外膜转运至关重要。
