RESUMO
In Escherichia coli, FkpA, PpiA, PpiD, and SurA are the four known periplasmic cis-trans prolyl isomerases. These isomerases facilitate proper protein folding by increasing the rate of transition of proline residues between the cis and trans states. Genetic inactivation of all four periplasmic isomerases resulted in a viable strain that exhibited a decreased growth rate and increased susceptibility to certain antibiotics. Levels of the outer membrane proteins LamB and OmpA in the quadruple mutant were indistinguishable from those in the surA single mutant. In addition, expression of P and type 1 pili (adhesive organelles produced by uropathogenic strains of E. coli and assembled by the chaperone/usher pathway) were severely diminished in the absence of the four periplasmic isomerases. Maturation of the usher was significantly impaired in the outer membranes of strains devoid of all four periplasmic isomerases, resulting in a defect in pilus assembly. Moreover, this defect in pilus assembly and usher stability could be attributed to the absence of SurA. The data presented here suggest that the four periplasmic isomerases are not essential for growth under laboratory conditions but may have significant roles in survival in environmental and pathogenic niches, as indicated by the effect on pilus production.
Assuntos
Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/fisiologia , Escherichia coli/enzimologia , Fímbrias Bacterianas/metabolismo , Peptidilprolil Isomerase/genética , Peptidilprolil Isomerase/metabolismo , Antibacterianos/farmacologia , Proteínas da Membrana Bacteriana Externa/análise , Escherichia coli/genética , Escherichia coli/crescimento & desenvolvimento , Escherichia coli/ultraestrutura , Proteínas de Escherichia coli/análise , Proteínas de Escherichia coli/metabolismo , Genes Bacterianos , Genes Essenciais , Imunofilinas/genética , Proteínas de Membrana/genética , Testes de Sensibilidade Microbiana , Mutagênese Insercional , Porinas , Receptores Virais/análiseRESUMO
Studies of the mechanisms that Gram-negative bacteria use to sense and respond to stress have led to a greater understanding of protein folding in both cytoplasmic and extracytoplasmic locations. In response to stressful conditions, bacteria induce a variety of stress response systems, examples of which are the sigma(E) and Cpx systems in Escherichia coli. Induction of these stress response systems results in upregulation of several gene targets that have been shown to be important for protein folding under normal conditions. Here we review the identification of stress response systems and their corresponding gene targets in E. coli. In addition, we discuss the apparent redundancy of the folding factors in the periplasm, and we consider the potential importance of the functional overlap that exists.
